Horizon (1964) s00e89 Episode Script

The Mystery of Murder: A Horizon Guide

This programme contains scenes which some viewers may find disturbing.
There are about 600 murders in the UK each year.
That's around two a day.
And, globally, about 50 people are murdered every hour.
Murder appals and repels us.
But it also fascinates.
So, what makes people murder? I felt like God.
The power of God over a human being.
I went into the kitchen and put my bowl of ice cream down.
I grabbed a knife from the counter, and I stabbed Larry and my mom.
Are some people born to kill? Or are they driven to it by circumstance? For 50 years, Horizon and the BBC have been following the work of scientists, as they struggle to delve into the minds of murderers, to try to understand why people kill.
The hope is that by understanding what makes people into murderers, we might, one day, be able to prevent it.
On the 21st December, 1997, a chilling murder took place in a quiet suburb in Ohio.
Dion Sanders had broken into his grandparents house, looking for money.
But they came home early and caught him in the act.
It ended up in a big argument.
A bad argument.
Next thing I know, I'm beating on them.
I mean, I'mI'm I remember I was in such a rage .
that they couldn't stop me.
A frying pan came into it.
To this day, I have no idea whether I grabbed it, or if they grabbed it to try to stop me.
Dion's grandparents had to defend themselves against an increasingly frenzied attack.
I knew grandpa had a shotgun in the house.
I remember looking through the door, and seeing grandma take the gun up off the floor.
I ended up getting the gun away from her.
I remember ending up behind her.
I remember loading the gun.
And I pointed at her and shot.
I remember her falling to the ground.
I remember reloading it.
I ran into the garage, I pointed at my grandpa and fired.
I don't know where I hit him.
I know I shot him.
For most of us, the idea of violently killing another human being, particularly your grandparents, is so abhorrent, we assume that anyone who is capable of it must have something wrong with them.
But is that right? Are murderers really that different to the rest of us? In the 1870s, science began to take its first faltering steps towards answering this question.
Dr Cesare Lombroso, the father of scientific criminology, was studying criminals imprisoned in Turin and Pavia.
'One November morning in 1871, 'Lombroso made what he thought was a great scientific discovery, 'when he studied the skull of the famous Italian thief 'known as Villela.
' 'I found in the occipital part, 'exactly on the post where the spine is found in a normal skull, 'a distinct impression, as an inferior animal's.
'In particular, rodents.
'I suddenly saw, lit up as a vast plain under the flaming sky, 'the nature of the criminal.
'An atavistic being who reproduces the ferocious 'instincts of humanity and of the inferior animal.
' Lombroso believed he had found evidence that a criminal's brain is different to that of a noncriminal.
A step back in evolution.
He claims that this was clearly displayed in the shape of a criminal's face.
'A criminal's ears are often of a large size, 'and the nose is frequently upturned, 'or of a flattened character in thieves.
'In murderers, it is often aquiline, like the beak of a bird of prey.
' Lombroso's approach was soon discredited, but it was the beginning of a big idea.
That criminals, and in particular murderers, have different brains to the rest of us.
The studies he conducted back in the 1800s, by today's standards might be laughable, but, at the same time, it was a beginning.
And what Lombroso did was open the door.
He built a foundation for others to build on.
But it was almost 100 years before science was able to provide the tools to really start exploring the mind of a murderer.
The first crucial step was research with animals, in the 1950s and '60s.
Scientists wanted to know if there were specific parts of the brain responsible for producing aggression.
In one ground-breaking study, cats were implanted with electrodes, and these were used to electrically stimulate different parts of their brains.
The animals, after such an operation, are perfectly at ease, and they suffer no discomfort.
And we can keep them like this for a long period of time.
But, when we stimulate, the first thing we see, with the smallest amount of current we can use, is this alerting behaviour.
The pupils are dilated, the ears are pricked, and the head might be raised a little.
The heart is working much harder, ready for the muscular exertion which we soon see if we stimulate a little bit harder.
'Then, when the current is switched on, 'the cat attacks the first object it sees.
'In this case, a dummy cat.
' Animal experiments like these provided strong evidence that specific parts of the brain are involved in producing violent and aggressive emotional reactions.
The key area is called the amygdala.
So, might the amygdala play a part in human violence and even murder? In 1969, the dramatic case of a patient known only as Julie gave scientists a rare opportunity to measure activity directly from the amygdala of someone who had come close to committing a murder.
Julie suffered from epilepsy.
During her fits, she often experienced fear and a sense of panic.
Then all the strange feeling would come over me.
Frightening feeling.
Strange and stronger than hell.
One day, while at the cinema, Julie was overcome by a fit and during that fit, she stabbed a young girl.
Luckily, the girl survived, but could Julie's epilepsy have been responsible for this violent attack? Dr Vernon Mark treated Julie after the incident.
What we did was to put a special guiding machine on to her skull, under general anaesthesia.
And I inserted a needle inside her temporal lobes, very close to the amygdala, and once we did this, we then recorded the electrical activity, trying to determine what site was firing off when she had her ordinary seizures.
Using a technique newly developed in animal research, the neurologists received signals transmitted by radio from electrodes implanted deep in Julie's brain.
They monitored her brainwaves during normal activity, while she was resting, and also during her seizures.
And then, more controversially, Vernon Mark's team reversed the signal.
And so, instead of recording activity, stimulated her brain.
Some seconds after the stimulation was initiated, the patient became unresponsive and she began to stare and then she had facial grimacing, almost characteristic of a primitive rage response.
And during this time, we noticed that the patient was producing electrical activity that looked like a seizure coming from the amygdala and quite suddenly, after some seconds of grimacing, Julie launched herself against the wall in a sudden attack behaviour, smashing her fists against the wall.
Julie's response to stimulation of the amygdala was strikingly similar to that of the cat's.
Her case proved there could be a direct relationship between a violent act and activation of the amygdala, the emotional centre of the brain.
Another unusual clinical case, that of Ted Bledsoe, was to implicate a totally different part of the brain in murderous behaviour.
Ted Bledsoe was a doctor, a model citizen with no history of violent behaviour.
79, 72 But then, he changed.
Gradually, over a ten year period, he became increasingly violent for no apparent reason.
I hit the child of some dear friends who, at that time, was about five years old.
He was teasing me and I hurled off and hit him in the face.
And I attacked my wife.
I knocked her down, got on top of her and beat her with my closed fists.
I know that had I a weapon in my hand, I probably would have killed her.
Finally, after losing everything, Ted was sent for a brain scan.
This revealed a massive tumour in his prefrontal cortex.
This is the part of the brain that allows us to control our reactions to the emotional impulses produced in the amygdala.
You can see that there is just no brain there.
There's supposed to be, but there isn't.
As Ted's case demonstrates, damage to the prefrontal cortex makes people less able to control their emotional reactions.
There's no way that somebody can say with a straight face that this fella, the absence of his frontal lobes has not had any behavioural effect on him.
That would be That's untenable.
By disrupting his impulse control, the tumour almost made Ted a murderer.
Cases like Ted and Julie's certainly suggest that the prefrontal cortex and the emotional centres of the brain are both involved in murder.
Yet, brain tumours and epilepsy rarely feature in murder trials.
So, is there other evidence that murders involve these two brain areas? The invention of functional brain scanning in the 1980s finally allowed psychologists to precisely measure the activity going on inside the brain of any murderer.
The first brain scanning study of murderers was carried out in California by British neuroscientist Dr Adrian Raine.
One of the attractions in coming to California is that one can obtain large samples of very violent and homicidal individuals.
Donta Page was one such murderer.
Aged just 21, he brutally raped and murdered 24-year-old Peyton Tuthill when she came home to find him committing a burglary.
'I was in the back, by the back door, when I heard the front door.
' At that time, she encountered the murderer, and there was quite a physical battle that ensued after that with her trying to protect herself and she got away.
'I chased her.
' But he didn't stop.
He proceeded to stab her many, many times.
What made Donta Page such a violent killer? Looking for answers, Dr Raine scanned his brain.
'This is the scan of a normal, non-violent person's brain.
'The warm colours, reds and yellows, indicate normal brain function.
'Donta Page's scan shows that his brain is not functioning properly.
'The colours are much cooler.
' What we can see in this lower scan is that Donta Page's prefrontal cortex is functioning much more poorly than that of normal people who are non-violent.
Dr Raine and his team scanned 41 murderers and all of them showed reduced functioning of the prefrontal cortex, the area which controls our response to our emotional impulses.
He also found that the emotion-producing centres of the brain, like the amygdala, which generates our aggressive impulses, were overactive in the murderers.
So, it seems that murderers have brains that make them more prone to rage and anger, while at the same time, making them less able to control themselves.
But it's more complicated than that because there are different types of murderer.
The ones in Dr Raine's study were mainly reactive, impulsive, hot-blooded.
Then, there are the cold-blooded ones, who planned everything in meticulous detail and may kill again and again.
So, what goes on inside the mind of a serial killer? David Krueger is a typical serial killer.
Like 90% of serial killers, he displays the psychological characteristics of a psychopath.
Aged just 17, he brutally murdered three young children.
'It all began on the 16th of September 1956.
'A little boy called Wayne Mallette had gone to 'visit his grandmother in Toronto.
'He was playing in the front yard, 'but when his mother went to look for him, he had vanished.
'Wayne was fascinated by trains.
'At some point in the late afternoon, 'he met with David Krueger.
Krueger lured him to a secret place, 'where he said they could wait for trains together.
'Six-year-old Wayne was led unsuspecting to his death.
'He was found a few hours later, brutally murdered.
'Despite a huge manhunt, Krueger escaped detection.
'Within three weeks, 'he persuaded nine-year-old Gary Morris to accept a ride on his bike.
'He led him to an empty waterfront area by Toronto Docks.
'When Gary was found dead later that night, 'he had been choked and viciously attacked.
' It is too bad that the two boys died, but I felt like God, with the power of God over a human being.
In the strangling of children, I found a degree and sensation of pleasure and of accomplishment that I didn't feel anywhere else.
David Krueger went on to kill four-year-old Carole Voyce before finally being arrested.
Now, had I for one instance thought, "This is a human being, this "is somebody who is been badly hurt by me," I think I would have stopped.
The fact that I didn't shows that those feelings were really secondary.
It's clear that David Krueger had no concern whatsoever for his victims.
And this is the key hallmark of a psychopath.
The essential features of psychopathy would include a lack of empathy.
I don't mean just a general I mean a profound lack of empathy.
A general callousness towards other people.
These are people without a conscience.
I didn't feel any sense of remorse or guilt at the time, I just wanted to create a balance.
Two boys had died, so maybe now a girl should die.
To try to understand why they have this extreme lack of empathy for others, Bob Hare began to explore the brains of psychopaths.
We actually showed our subjects a series of pictures and some of these pictures are neutral and rather innocuous, others are horrific, appalling, would make most people extremely upset.
They were very distressing.
Hare looked at the psychopaths' emotional brain, while they were looking at the images.
The results were striking.
'This is a scan of a normal person looking at violent images.
'The red shows a great deal of activity in the amygdala.
'By contrast, the psychopath has almost no activity.
'There was no difference in the way they processed neutral 'and emotional images.
' This lack of emotional activity in the amygdala in response to seeing others' suffering explains the chilling lack of empathy psychopaths have for their victims.
I remember jumping on the hillside, up and down, with excitement, chanting, "Die, die, die," as she was lying there dying.
Scans also revealed that unlike reactive killers, the prefrontal cortex functioned normally in psychopaths.
They can control their aggressive impulses.
And it's this combination of self-control with no empathy that makes them so dangerous.
They can carefully plan their attacks without being held back by concern for their victims.
So, scientists had uncovered what is different about the brains or reactive killers and psychopaths.
But there is another type of killer - those who suffer from schizophrenia, and only kill while in the grip of madness.
In the Western world, 5-10% of murders each year are committed by someone with schizophrenia, as was the case with Cody Mitten.
As Cody was growing up, he was a really good little brother - loving and energetic and he just He was a great kid.
I was very proud of Cody.
You couldn't ask for a better son.
Even growing up, he was very lovable, understanding and helpful.
You need some help? He'd help you.
He was number one son.
He had a real close relationship with his mother.
He loved his mother very true.
I mean, there was no doubt in nobody's mind that he loved her.
But in 1997, Cody started acting strangely.
That night, he just shows up at my place.
He's holding his stomach, he's saying that he's sick and he thinks he's going to die.
And that he thought he was Jesus Christ.
Out of the blue, he would come out and say that he was half man and half ape.
He started talking and saying weirdthings, which was not becoming to Cody.
I was scared because there was such a drastic change in him.
Though most schizophrenics are not violent, having schizophrenia makes men three times and women 22 times more likely to murder.
In Cody's case, his illness drove him to kill his mother and her boyfriend Larry.
We're all sitting in the living room and stuff and I was hearing voices come out of the TV, like they were talking to me, telling me that people were trying to kill my family, trying to kill me and stuff.
None of this made sense to me at all.
I was just really fearful.
Even though my mother was everything to me, at this time, I thought she was in cahoots with everybody else, trying to kill me, trying to do harm to me and stuff.
So, I went into the kitchen to put my bowl of ice cream down and In the kitchen sink.
And I grabbed a knife from the counter and I stabbed Larry and my mom and I don't know why I don't know.
I don't know OK.
I stabbed Larry and my mom I don't know why.
I have no idea why.
Um To try and understand how schizophrenia could make someone more likely to kill, scientists scanned the brains of schizophrenics.
The scans revealed that the emotional centres of their brains did not respond normally to the emotions of others.
And their prefrontal cortex did not function properly either.
Schizophrenic murderers seem to combine the lack of empathy of a psychopath with the lack of impulse control of a reactive killer.
The use of brain scans has allowed us to identify two areas of the brain.
One that produces emotion and one that controls our response to emotions, which appear to malfunction in the brains of murderers.
Alongside this, scientists have also studied the biochemistry, which seems to underline these malfunctions.
They wanted to see if there were any chemical imbalances affecting the brains of murderers.
The first and most obvious target was the male hormone testosterone.
Because perhaps the most striking about murder is that 90% of murderers are men.
So, might testosterone play a part in creating a killer brain? An important clue came from a notorious serial killer in Connecticut in the 1980s.
'Michael Ross says a powerful 'and irresistible urge to hurt women could come over him at any time 'and at any place, for no apparent reason and with no warning.
' 'You cannot imagine what it is like 'to be excited and to be stimulated 'by thoughts of killing somebody, 'by raping and killing and degrading.
' They are extremely stimulating and satisfying in the short term, but they're disgusting as hell and I wish that I didn't have them.
Michael Ross was diagnosed as having abnormally high levels of testosterone.
So, could there be a link between high testosterone and violent crimes? This question led Professor James Dabbs to collect and test saliva samples from hundreds of prisoners.
We examined prison inmates and looked at the testosterone level and related it back to the crimes they had committed and found that the higher testosterone inmates had more often committed violent crimes.
Of course, not everyone with high testosterone is a killer.
But high levels of it do make violence more likely.
And the very latest research has found that giving normal men extra testosterone increases the reactivity of their amygdala, the emotional centre of the brain which scanning had revealed was overactive in many murderers.
This could explain the link between testosterone and violence.
Meanwhile, scientists were also investigating another chemical that they suspected might be implicated in murder - serotonin.
It's a neurotransmitter that is important for the functioning of the prefrontal cortex, the area of the brain that is crucial for regulating our emotional impulses.
The first clues came from studies with monkeys.
If you look at monkeys who have low serotonin, then what you see are monkeys that have what we call an antisocial personality.
These are monkeys that nobody wants to associate with because they're likely to beat up other monkeys, or likely to do the kinds of things that really are an unpleasant kind of relationship to have.
So, scientists wondered if the same might be true of humans.
'Striking evidence came from a study of Marines who'd 'served in Vietnam, but whose behaviour was causing concern.
'The clue to their overtly aggressive behaviour was 'discovered for the first time by Dr Fred Goodwin 'when he studied hundreds of Marines whose violent behaviour went 'well beyond the call of duty.
' We dug into their charts and found that there was lots of histories of violent and aggressive behaviour in many of these individuals.
He found the violent men shared a key characteristic - unusually low levels of the brain chemical serotonin.
It's a modulator, a dampener, and it is a brake.
It's a brake and so low serotonin seems to take the brakes off.
His discovery that low serotonin can increase violent behaviour was a scientific turning point.
Could a lack of serotonin allow some men to kill? The case of Deion Sanders, who had brutally murdered his elderly the grandparents, provided further evidence that serotonin could play a part in murder.
In prison, Dr Paul Ross measured Deion's serotonin levels.
A very abnormally low level of serotonin has been linked to many impulsive disorders including aggression, unopposed aggression, or rage.
In the case of Deion Sanders, his serotonin level was very abnormally low, extremely abnormally low.
Extremely low levels of serotonin put Deion amongst an unknown number of men with a heightened risk of losing their temper, capable of sudden and unrestrained violence, capable of murder.
Over the last 50 years, we've discovered a number of biological differences between the brains of murderers and the rest of us, but what causes of those differences? Is there a genetic component or is it entirely environmental? Are murderers born or are they made? Initially, scientists focused on the role of upbringing.
Experiments with monkeys in the late 1950s and early 1960s revealed the importance of motherly love for the normal psychological development of baby monkeys.
In controversial experiments, Harry Harlow put baby monkeys in isolation for up to a year.
All the monkeys came out severely disturbed.
Lack of normal parental care had clearly affected their emotional development.
And it looked like the same was true of humans.
Certainly it had been known for some time that murderers often had violent and disrupted childhoods.
Steve Parkus is a classic case of what a terrible childhood can do to someone.
Steve and his brother were abused and neglected by their alcoholic parents.
She was harder on Steve than she was on me, cos I was the youngest, probably.
I always hid behind him cos he was bigger than I was, right? She started swinging, I just ducked behind him, right? In lieu of a baby-sitter, when Linda went out drinking, she would just lock the kids in the bathroom, lock the door.
One time, Steve and Chester sneaked out, out the bathroom window, and the police found them and brought them home and after they left, she heated up a knife over the stove and started burning them on bare buttocks with the hot blade of the knife and that was the point at which the juvenile authorities became involved in the case.
The two boys were taken in by their uncle Taylor and aunt Bernice.
Unfortunately for Steve, it was like out of the frying pan and into the fire.
He was taken away from a schizophrenic mother and put in the home where he was raised by a sadistic paedophile.
Steve Parkus is a very good example of a combination of some of the most horrendous abuse that you can possibly imagine, sexual and physical, leading to a completely unsocialised individual.
He was a person who was raised absolutely and totally without any love, without any affection, without any caring.
He was used as a thing from the time that he was born until today.
Aged 17, Steve Parkus ended up in prison.
The first day that he got to prison, the guards stripped him naked and marched him up and down the cell block and auctioned him off to the highest bidder.
He was sold as a sex slave for $60.
CLOTH TEARS In November 1985, while still in prison, Steve murdered Mark Steffenhagen, his only friend.
I put his hands tied his hands and tied his feet .
and I laid him over on his back and I told him what I was going to do and why.
And I just started choking him, you know.
I had my hand around his throat.
It seemed obvious that a violent, unloving childhood played a crucial part in creating a killer, the question was how? In 1961, a groundbreaking experiment revealed the effect that exposure to violence could have on young children.
This four-year-old given a Bobo doll to play with for the first time shows no tendency to attack it.
The idea doesn't seem to occur to him and he didn't do so even though he was allowed to play with the doll for a considerable period.
In the experiments, the children were allowed to watch an adult attack the doll violently.
This particular four-year-old was not only generally unaggressive, but he hadn't previously learnt to punch.
But when given a second chance to play with the doll, he not only attacked it eagerly and without prompting, but copied with surprising accuracy the techniques of attack he'd just witnessed.
This behaviour parallels This may seem obvious to us now, but at the time it was a revolutionary finding.
Witnessing violence made children behave more violently.
But it's not just a case of children copying adult behaviour.
We now know that childhood experiences actually affect the development of the brain areas involved in controlling aggression.
Professor Peter Smith is an expert on child psychology.
He's studying the development of early aggressive behaviour.
They know that they each want the scooter Yeah.
but they're not able to really inhibit those impulses yet.
That's because of a lack of brain development, compared to older children.
Until the age of three, our impulses run riot.
There's no stopping the urges which come from the emotional centre, but then we start to develop the part of the brain that allows us to the control our aggression, the prefrontal cortex.
Yet, crucially, how well this control mechanism works depends on our experiences.
What do we do at the nursery? We share.
Leon, Kelvin, when the sand timer finishes - tell me when it's finished and we can take turns on the bikes, yeah? Incredibly, being taught to share and take turns actually changes the physical structure of the brain.
It strengthens the connections between the emotional centre and the prefrontal cortex.
This is what makes us less aggressive.
It's actually children as young as two who are the most frequently aggressive, physically aggressive, and they're gradually learning not to be aggressive in that way through a socialisation process.
So childhood experiences actually shape the very parts of the brain that scanning had revealed don't function properly in murderers.
If someone grows up experiencing only violence, these brain areas are unlikely to develop normally and it is more likely that they too will become violent.
POLICE RADIO CHATTER As well as disrupting the normal wiring up of the brain, studies in the 1990s suggested that childhood abuse might also be creating killers by actually causing physical damage to the brain.
A lot of these kids have been just thrown downstairs and battered against walls, punched, hit, and so the brain itself is damaged.
Let's get a path for the The prefrontal cortex is especially vulnerable.
If you're an infant and your parent vigorously shakes you and your head rocks backwards and forwards, the brain inside the skull - if this is the skull and this is the brain - it will bang on the bony part of the skull and this frontal part of the brain here will get damage as it's rocked backwards and forwards inside the skull.
Donta Page who had brutally murdered Peyton Tuthill in 1999 is a textbook example.
As a baby, he was frequently shaken by his mother and as he got older, the abuse got worse.
What are you doing? Come here! His mother began to use objects to hit him with, including, um, electrical extension cords, shoes, whatever was handy.
These were not once-a-year beatings, they were beatings that occurred almostdaily.
This physical abuse could help explain the malfunctioning of Donta's prefrontal cortex.
I would tend to be persuaded by the notion that the early physical abuse, amongst other things .
could likely have led to the brain damage which could likely have led to him committing this violent act.
As the evidence mounted, it seemed clear that killers were largely being created by their violent upbringing.
But only a small proportion of those who have terrible childhoods grow up to become murderers.
Now, studies with twins and adopted children had already suggested there is a hereditary component to violence.
Could it be that there are genes that predispose us to murder? The breakthrough came in 1993 with a family in Holland where all the men had a history of violence.
15 years of painstaking research revealed that they all lacked the same gene.
There was one gene that was missing and in the men and all these men were violent .
so that kind of supported the idea that one gene really controlled a behaviour.
This gene produces an enzyme called MAOA.
It regulates the levels of neurotransmitters involved in impulse control.
It turns out that if you lack the MAOA gene or have what is known as the "low activity variant", you are predisposed to violence.
This variant became known as the warrior gene.
And soon after, a gene was discovered that controls the levels of serotonin.
This was the neurotransmitter linked to violent behaviour in monkeys, marines and criminals, like Deion Sanders, but is having the warrior gene or the gene for low serotonin enough to make you a killer? For Professor Jim Fallon, this question was about to become deeply personal.
Jim had been researching the brain abnormalities of murderers for 11 years, when, one day, a casual conversation with his mother revealed a history of murder in his own family.
As we were discussing this, and different brains, I said to him, "You should look into your own history.
" I mean, it was really pretty startling, but, you know, I knew it was true because she doesn't make things up.
Yeah, there were quite a few murderers in that family.
At least 16 murderers in the one line.
Hearing this, Jim took the bold decision to run a check on the entire family for the genes linked to violent psychopathic behaviour.
Back came the results.
Everybody had a mix of things in our family.
It looked like an average sort of mix of these different genes that have to do with aggression and all sorts of behaviours, except now and again there was this one that showed all of these high-risk genes and it was mine.
People with far less dangerous genetics become killers and are psychopaths than what I had, you know.
I had, like, almost all of them.
It was right up But the reaction from his family was to unsettle him even further.
'I knew there was always something off.
' It makes more sense now that it's clear that he does have the brain and genetics of a psychopath.
It all falls into place, as it were.
Those are 'I have characteristics or traits, 'some of which are, you know, that a psychopathyeah.
' I could blow off an aunt's funeral if I thought there was a party that day - I would just take off and that's not right.
The thing is I know that now but I still don't care and so I know something's wrong, but I still don't care.
And, er, you know I don't know how else to put that.
It's just you are in a position where, "Oh, that's not right "and I don't give a shit," and that's the truth.
But Jim isn't a murderer, he's a respected professor.
It turns out that about 30% of men have the warrior gene and 16% have the low serotonin gene and clearly most of them are not killers.
So why isn't everyone with killer genes a murderer? The answer is that whether the genes are triggered or not will depend on what happens in your childhood.
'If you have the so-called high risk form of the gene' and you're abused early on in life, 'your chances of spending a life of crime are much higher.
'If you have the gene, the high risk gene, 'but you weren't abused then there really wasn't much risk,' so just the gene by itself, the variant, doesn't really dramatically affect behaviour, but under certain environmental conditions, a big difference, and that was a very profound finding.
So what was it about Jim's environment that cancelled out his unlucky genes? It turns out that I had an unbelievably wonderful childhood.
I'd go back and look at old movies and old pictures and I'm smiling and I'm as happy as a lark and you can see it all the way through my life.
You know, there's a good chance that that offset all these genetic factors, the brain development and everything and it washed that away.
So it seems that a genetic tendency towards violence together with an abusive childhood are a killer combination.
Murderers are both born and made.
We now have a far more sophisticated understanding of the complex interactions between the social and the biological factors that predispose people to murder.
But what can we do with that knowledge? Can we use it to reduce the risk that murderers will reoffend or perhaps even prevent them from killing in the first place? As far back as the 1950s, we had the ability to use drugs to treat some types of potential murderer and reduce the chances of them killing.
Schizophrenia, in particular, can be successfully treated with anti-psychotic medication.
Cody Mitten had killed his mother while suffering from delusions and he was sentenced to life in prison.
Cody was obviously psychotic because when you went back and looked back at the past, two weeks prior to the incident, he started to have definite psychotic symptoms, believing that auditory and visual hallucinations along with delusions.
He believed that voices were coming out of the TV telling him to hurt and he believed that others were trying to hurt him.
While in prison, he has been receiving treatment for his schizophrenia and as his symptoms have receded, the enormity of what he did has sunk in.
Oh, man, erm HE SOBS Oh, I just wish everything was the way it used to be, but it's not, no.
While his illness is being kept at bay, Cody is unlikely to kill again.
But perhaps his mother's murder could have been avoided in the first place.
I could see it in his eyes, I felt like Cody needed to go to the doctor and we needed to take him today.
Cody's mother took him to the hospital, but tragically they sent him home.
They said everything was normal and I said, "That can't be.
" That night, he killed his mother and her boyfriend Larry.
Had the doctors detected his schizophrenia and kept him in hospital for treatment, they might still be alive today.
The discovery that brain chemistry was involved in certain murders has also led to the development of drugs to treat these chemical imbalances.
How do you admit that you are sexually stimulated by killing someone? In particular, drug treatment appears to be effective when testosterone is implicated in the crime.
It's, er, it was like a monster inside me.
It's so tempting just to give into it.
Michael Ross had abnormally high levels of testosterone when he killed eight women in the early 1980s.
In America, male offenders like Michael are given drugs to lower their testosterone levels.
It's known as chemical castration.
Michael's testosterone levels fell to 5% of that of most men.
Writing for a scientific journal, he described the effect of the treatment.
"My obsessive thoughts and urges and fantasies began to diminish.
"The problem is still there.
"It's easier to deal with because it isn't always in the foreground, "intruding on my everyday life.
"The monster within is still present "but the medication has rendered him impotent.
"Had I begun receiving just a 1cc injection "once a month 15 years ago, eight women would be alive today.
" Studies of violent sex offenders have shown that chemical castration cuts reoffending rates to below 5%.
As well as pharmaceutical interventions, scientists also use psychological therapies to try and rehabilitate murderers.
Now, it certainly reduces violent behaviour in many offenders, but psychopaths provide a cautionary tale.
In the 1970s, a group of psychologists in Canada were using therapy to treat psychopaths.
When I arrived at this hospital in 1975, the pride of the hospital at that time was this programme for psychopaths that was run on four wards of Oakridge.
And it was considered by everyone at the time to be an excellent, excellent programme that would be especially beneficial for psychopaths.
David Krueger was one of the psychopaths on the programme.
Krueger himself was deemed greatly improved.
After over 30 years in a maximum security mental hospital, he was sent away to a less secure institution at Brockville.
Marnie Rice and her colleagues followed up treated patients to check on the treatment programme's success .
but when she compared re-offence rates of psychopaths who had been treated with psychopaths from prison who had received no treatment at all, there was a surprise.
When we looked at the results and what we saw was the programme actually made the psychopaths worse, we were astounded.
I mean, I looked at these data and I thought, "There's got to be a mistake here.
" You know, we went back and we checked and checked and checked and sure enough, the effect was real.
It was absolutely the case that the programme made the psychopaths worse.
Many psychopaths have described the therapy programmes as finishing schools where they honed their skills.
I did learn how to manipulate better .
um .
I did learn how to get control of expressing my feelings inappropriatelybetter .
and keep the more outrageous feelings under wrapsbetter.
On his first day pass in 35 years, David Krueger brutally murdered a fellow inmate.
For the time being, it seems we cannot treat the psychopaths' underlying lack of empathy.
Scientists are now focusing on using therapy to try and prevent murderers being created in the first place.
They know enough about the causes of murderous behaviour to spot early warning signs, and attempt to intervene before it's too late.
The hope is that therapy will undo some of the psychological damage being caused by an abusive childhood and prevent children from turning into killers.
Children, like Justin and his brother Cody, who spent their first few years in a violent home.
When Justin was only two years old, his mother was murdered.
There was a verbal argument that started between the boyfriend and the mother and it led to physical confrontation when they were shoving and pushing at each other and then the boyfriend got enraged and started to beat her and she kicked at him and he picked up a knife and apparently stabbed her in the chest.
Be careful, Cody.
Justin was there when his mother was murdered.
He's seen everything and he was real devastated.
You know, he'd just cry a lot and scared to go upstairs to his room, scared to sleep at night.
He had to sleep with us, er, he just wasn't Justin again.
He wasn't a happy child at all, nothing like that again.
Stand up straight.
Justin was sent to see Dr Bruce Perry who works with children from abusive families.
You're taller than you were last time you were here.
I saw him very soon after the event and had him come into our office .
and just getting at or even mentioning mother resulted in this tremendous, explosive, what I would consider, re-enactment behaviour.
And I think in many ways, his behaviours were not necessarily re-enactment of the murder, but they were re-enactment, I think, of the kinds of domestic violence that he had seen prior to that.
Luckily for Justin, he's receiving the help he needs to reverse the damage.
In the 18 months he's been attending Dr Perry's clinic, he's made great progress.
Back on track.
It's going to be a slow process but his future is going to be real bright, I can see that.
We know a huge amount about what happens inside the minds and brains of murderers that have been caught, but we are still some way off being able to predict who will become a murderer.
There are far too many factors involved.
One thing, however, is certain, we will continue to be fascinated and appalled by their terrible crimes for many years to come.