Hi I’m Wendy Zukerman. You’re listening to Science Vs from Gimlet Media. This is the show that pits facts against foul play. On today’s show, serial killers.  

A quick warning before we get started, in this episode we’ll be discussing homicide, and sexual violence. Please take care when listening to the show. And if you’re feeling depressed or you just want to talk to someone, in the US, you can call the National Mental Health Helpline at , 1-800-662-HELP (4357)[1]. That’s 1-800-662-HELP. That number will be on our website, along with other resources.

OK, onto our episode. We think of serial killers as relentless predators who kill over and over again. And who seem to relish it. They are the ultimate boogy-man… our worst nightmare…… except they are real. And one infamous murderer who embodies a lot of our fears about serial killers is a guy named Ed Kemper, who killed his victims in the 1960s and 70s.   He’s the kind of murderer we picture when we think about serial killers: smart, ruthless, and all around super creepy. And on today’s episode we’re going to try to understand what makes a guy like Ed Kemper tick.

WZ Can you tell us about Ed Kemper

EH Oh yes oh yes I can tell you about Ed Kemper. EH and by the way you would like Ed. and I think he’d like you.

WZ why, cause I’m female? EH Yes. but then he’d probably kill you

Okaaaaay. So. That guy … is actually a researcher… His name is Eric Hickey, and he’s a criminal psychologist at Walden University. And like a lot of people, he’s really fascinated by serial killers ... like Ed Kemper. Eric he told us that Ed started killing early, when he was only 15[2].

He said one day I came down from breakfast, and I thought what would it be like to shoot grandma. Got a rifle and shot and killed her

He killed his Grandfather too. And then Ed turned himself in[3] and ended up in a state psychiatric hospital. Ittt  n the late 60s he was released on parole at the age of 21[4]. [5].  Ed was grown up and back in the outside world. He looked kind of dorky and unassuming, he wore these thick glasses. But he was really smart[6], and he was huge.

 6 foot 9 and 300 pounds[7], he a big guy

And it didn’t take long before this big guy… started getting violent again. In May 1972 [8][9] He picked up two young female hitchhikers asking for a ride.  And Ed was charming…

EH And they would get in the car...   because he was such a nice guy and he would take them off into the woods and he would kill them…

Ed drove those two hitchhikers to a remote area and parked the car. Then he killed them both[10][11]. After these women ... Ed kept going. He killed four more young women within just a few months

Kemper was killing college students as fast as he could, 

Oh my gosh

And all the while...he was living what appeared to be a perfectly normal life. Even his psychiatrist was fooled. Eric told us this one story about when Ed visited his therapist.

<<EH He sits down with therapist started telling him about how pleased they were… doing so well ...without you i wouldn’t be here...he thanked them during that interview in the trunk of his car was the head of a college student

WZ GASP

Yes, Ed often decapitated his victims and kept the heads. Sometimes he had sex with them....the heads.[12] In total, Ed Kemper murdered 10 people[13], including his mother… before turning himself in to the police.

We’re telling you this story because Ed Kemper, he’s our monster: a cunning predator who lures women into his traps  He’s so quintessential that there’s a character based on him in the TV show MindHunter. And the creepiest thing about it… while Ed is now in prison[14]… there are other serial killers out there[15].. Right now.

 So what do we really know about them?  What drives a serial killer to do what they do…?

When it comes to serial killers there are lots of creepy stories but then there’s science

<AHHHH>>

Science Vs serial killers is coming up right after the break.

BREAK

Welcome back.. So on today’s show we are finding out… what do we really know about serial killers?  

Researchers estimate that over the last two decades… there are have been almost 500 serial killers[16]running around the US … nine out of ten of the are men … And by they way according to the FBI you’re considered a serial killer if you kill at least 2 people - in separate events[17][18]. So our first question is this: other than killing… what else do serial killers do? Because on TV and in the movies ... they do some weird and twisted things alongside the killing.

Like in the Mentalist, this serial killer would always paint a " smiley face" in the victim’s blood somewhere near the crime scene.

Drawn in the victim’s blood. Clockwise, with 3 fingers of his right hand, with a rubber kitchen glove.

There are so many examples, in Silence of the Lambs, the killer puts moths in his victims’ mouths, and in the Wire to imitate a serial killer McNulty tied red ribbons to several dead men.

WP oh it's repeated ad nauseam, in TV and movies on serial killers,

This is Wayne Petherick, a researcher of Criminology at Bond University in Australia[19]….

And he told us that when it comes to the weird stuff the serial killers do… Hollywood isn’t totally off… but it’s complicated. So for example… one study[20] of 90 serial killers analysed the stuff they did other than killing...  They wanted to know

WP Did they steal something from the crime scene, were there bite marks, did they disfigure body or engage in other mutilation behaviours

And the researchers found that often serial killers did more than kill. A lot of the time they sexually assaulted their victims[21], But the killers also did other stuff… like dismembering their bodies. Researchers found that 40 percent of the time they dismembered their victims, and about 30 percent of the time they scattered the body parts[22]

So what makes them do this weird stuff? Hollywood presents it all as some master plan, or the killer playing out some creepy fantasy … But Wayne says sometime the explanation might be a lot simpler: they just wanted to kill someone … and now they’re covering their tracks.

So you might dismember a body because it's some fantasy that you have, or you might dismember the body to help you dispose of the body-01

Wayne has seen people jump to fantastical explanations for creepy behaviour … but he says that can be a mistake.

The general rule is always function over fantasy, always consider function before you think whether or not it has a fantasy element to it-[23]01

Still though, it’s clear that not everything serial killers do is functional. A study of almost 40 serial killers, using data from the FBI, found that 70 percent of them did some things to their victims that would be very hard to explain as anything other than fantasy[24] - like carving a pattern into the victim’s chest, or leaving them in weird poses. That’s just one study, though, so it’s not really clear how often this happens. But bottomline: the movies might get this one right. Serial killers can do weird stuff on top killing their victims.

What the movies get wrong though - is that most serial killers don’t seem to do the same weird thing to their victims everytime, every single time they kill. Several studies have found this ...  that more often than not, they change it up.[25].[26] 

Those kind of signature behaviours don’t tend to occur with as great a frequency was we are led to believe.

In fact, for a while there was a popular idea that cops might be able to catch serial killers by looking at crime scenes and finding patterns: but it doesn’t usually work. A study of 200 serial killers found the most common way for serial killers to get caught was someone they knew turned them in[27].

I think the idea that every SK leaves an ace of spades playing card behind at a crime scene is very different from the reality, which is really just that they are really just somebody who is inclined to kill multiple times-01

They are just somebody who is inclined to kill??? Multiple times??? What’s that about?  

For many of us, the idea of killing someone is horrifying. And yet serial killers do this over and over again...[28] [29] [30]. WHY? Well, to get at what drives serial killers... we went back to our criminal psychologist Eric Hickey… who we met at the beginning of the show. He’s the guy who really enjoys his research into serial killers…

I just really like the dark side, because I need to know what people are like, what makes them tick

And Eric is kind of the perfect person to talk to about why serial killers do what they do… he’s analysed hundreds of cases and interviewed about a dozen serial killers, personally.[31]...  

Why do they say they do it? Do they have clear reasons?

EH usually not Most of them don't have the insight or they’ve never really thought about it that deeply.

So for example, Eric told us about the time he tried to understand the motivations of this killer called Larry DeWayne Hall, who’s believed to have killed dozens women in the 80s and 90s[32]...  And so they sat and talked…

I was sitting there my left leg was touching his right leg. That’s how close I’m to Larry, he’s got this long beard and this crazy look in his eye.

And at first … it wasn’t clear why Larry had killed so many women, until Eric dug deeper… He asked him.

I said so Larry, do you have a girlfriend… ? NO Have you ever had sex with a woman? No. So now the big question was, the million dollar question, I said Larry, have you ever had sex with a dead person. And he looked at me and he smiled and said well maybe-03 larry was killing his victims and as soon as he killed them he had sex with them because they were still warm so to him it was like they were still alive.

Right… a lot of serial killing seems to be sexually motivated[33][34][35][36] -  as we said - a lot of serial killers rape their victims before killing them.[37][38] While, some of them - like Larry, have sex with them afterward… And although necrophilia among serial killers is rare[39]… it’s hardly unheard of. [40] [41][42] [43]

It's not always about sex though ...some serial killers do it for good old fashioned greed, like collecting insurance money. Others claim to be politically motivated[44] [45]..[46],

But ultimately…  two large surveys found that the most common reason people do this is because they get some enjoyment out of it… for sexual reasons or otherwise[47].

Like the Zodiac killer, who killed at least 5 people . He wrote: I LIKE KILLING PEOPLE BECAUSE IT IS SO MUCH FUN.[48]

So what made them this way - how do you become someone who enjoys killing over and over again?

That’s coming up… after the break.

BREAK

Welcome back, we’ve just learned that many serial killers murder people over and over again - because they get some pleasure out of it. Which is unnerving … and it’s one of the things that makes serial killers so scary. So our next question is what makes a serial killer? How does someone become a person who can do these horrifying thing?

One idea from Hollywood is that Serial Killers are evil geniuses…who get off on killing because they see themselves as higher up  in the food chain. The rest of us are like prey - scurrying around - for them to catch. Like here’s Kevin Spacey’s character describing how he saw his victims in “Seven.”

<<An obese man, after him I picked the lawyer, only in a world this shitty could you even try to say these were innocent people and keep a straight face… >>

And this idea… of serial killers as intelligent masterminds… preying upon weaker victims shows up in true crime docos all the time...

<<Malicious masterminds. They are among the most devious and twisted of killers...their intellectual acumen is their greatest weapon. It enables them to plot elaborate crimes and elude capture.>> 

So let’s tackle this idea that serial killers are evil geniuses. To find out if this is true … our reporter Shruti Ravindran spoke to  Gwen Adshead (AD-sed), a professor of psychiatry at Gresham College in the UK[49] [50]. And Gwen has been working with murderers and violent offenders for more than a decade[51][52].[53].

<<SR i have to ask when you find yourself sitting next to a chatty person on a plane what do you tell them you do-02?

 ah laughter well i don't usually tell them what i do usually tell people i'm a florist.

Why a florist?

Why a florist? Well i love flowers would love to be a florist do flower arranging, I think that would be wonderful And talking about flowers usually preferable to talking about murder and violence>>

But on this show we prefer to talk about murder and violence. And in particular, whether serial killers, are smarter than the rest of us.

 

<<SR People think of serial killers as evil geniuses who are diabologically intelligent,

GA: yeah

SR what do we know about whether that's true-01

GA well we don't have any evidence that's true

Gwen told us about this one database where researchers gathered together the IQ scores of more than 300 serial killers, mostly from the US. And while IQ isn’t a perfect measure of intelligence, it’s one of the best we’ve got. The researchers found that most of these serial killers are about as smart as you and me — on average, probably a little dumber[54]. Another study found they were actually a bit above average[55]. Overall… Gwen says:  

GA most of the people who've been identified as serial killers have been of average intelligence>>

Average intelligence[56]. Now, there are some super-smart serial killers - like Ed Kemper, the guy with the head fetish.[57] He was said to have an IQ of  around 140[58]. That’s just shy of genius-level! But he is the exception rather than the rule.

<<GA the idea that there are a lot of evil geniuses running around plotting to kill people is not really borne out by the data. 

Ok so when it comes to smarts… serial killers are mostly average... Not intelligent masterminds. And even this whole Hollywood trope[59] is kinda dumb… if you really think about.. I mean, why would being really smart explain away their sadistic impulses?

Sonext idea: are they just straight up deranged? Well, what’s interesting is that most serial killers aren’t diagnosed with any kind of obvious mental disorder[60] — until they’re found killing a bunch of people.[61] [62]. One study of more than 250 serial killers found that only about 20 percent were diagnosed with a psychiatric disorder before getting arrested for their crimes [63]...  So they walk around among us… just blending in.

Which bring us to another idea that people reach for to explain serial killers’ behaviour… this idea that serial killers are psychopaths. They seem normal, but they’re secretly… manipulative, calculating and without emotions. Think about  Christian Bale’s character in American Psycho.

 

<<I have all the characteristics of a human being: blood, flesh, skin, hair; but not a single, clear, identifiable emotion except for greed and disgust. >>

Not a single emotion. Classic Christian Bale.  But seriously, the word psychopath gets thrown around a lot…[64]. A big thing it signals to a lot of people - is this lack of empathy. That serial killers do what they do because they don’t feel bad when people suffer. So that’s what we’re going to focus on.[65].  [66]… do these killers lack empathy…?

When documentary filmmakers asked Ed Kemper about this idea in the 1980s… he said he did feel bad... especially when it came to killing his own mother.

<<Ed Kemper: And it’s so hard, so cold...and that’s the first time bin ten years i looked at it that way, that intensely, that honestly. It hurts cause I’m not a lizard.. I’m not a rock.

So that’s what Ed said… but what can the science tell us… about serial killers and empathy?  Well, there isn’t reliable research on whether serial killers in particular lack empathy[67] [68].. But there is some research on other violent criminals[69] . And our psychiatrist, Gwen says that on the whole low empathy doesn’t seem to explain violence generally.

<<To suggest that you're generally low in empathy on a day to day basis I think jury is pretty out on that one because different studies show different things>>

So for example, a review paper of 35 studies - found that while some research showed a link between violent people having less empathy, others didn’t see this… And overall they said this idea can’t clearly explain violence.

And this conclusion was also borne out in this kind of remarkable study that followed more than 1000 juvenile offenders for several years[70] and it tried to see what’s special about the ones who ended up becoming killers. And so called psychopathic tendencies - lack of empathy, being callous - that didn’t predict if they would go on to kill[71].  What it did find, though .. Is that if the kids grew up around violence[72]…  that increased their chance of becoming a killer. And Gwen suspects that this is true for serial killers as well

<<I mean I think it's very likely though that a man who becomes a serial killer is likely to have been exposed to violence himself I suspect in childhood. I think it's quite difficult to just start up a career of violence without having been exposed to it in some way.

Which takes us to the most concrete clue we could find in the literature to help explain serial killers… serial killers do have a higher chance of being abused as kids… compared to other people.  [73][74][75][76] . And that includes all kinds of abuse - physical, sexual and psychological. This is true for Ed Kemper, the guy with the heads, he’s said to have grown up in an abusive home … his mother would lock him in the basement for hours as punishment[77].

But before you go blaming mum and dad for the whole kit and caboodle…. This can’t explain everything ... not all serial killers were abused as kids.  One study of 50 serial killers  found that about two-thirds had been abused … leaving a third who hadn’t[78].[79],[80],[81] So who knows what’s going on there?

i think one of the myths about serial killers is we know a lot about them and i'm not sure we do know a lot about them because they’re so unusual…

So if you break it down … there’s been an average of 50 serial killers running around in the US each year for the last few years… 50. But still these killers are extreme outliers … when you zoom out to the American population, there’s roughly one serial killer for every 6 and a half million people ...[82] And the fact that they’re so outside the norm makes it really tough for science to explain them…

But still… when it comes serial killers, what do we know?

Unlike in the movies... they don’t often do this weird ritual thing to every one of their victims… they actually switch it up quite often

We know that many seem to be driven by sex … and they often sexually assault their victims alongside killing them...

Serial killers are often not evil geniuses - Most of them have an average IQ.

And Gwen says we can’t really say too much more about serial killers than that…

It's very hard to say anything sensible about them such a bizarre and unusual way for people to behave they’re statistically just off the map …

Even though serial killers are statistically off the map…they might feel like a threat … because they’re all over our movie screens and in the news … but the truth is … your chances of being taken out by a serial killer are super small… like if you’re a woman, statistically, you’re waaaay more likely to be killed by a current or former male partner than anyone else.[83]. So… while some might be worried about the boogeyman under the bed… really we should be worried about the person we’re in bed with.

<<but we don't want to think about that we would much prefer to think about the homicidal equivalent of ghoulies and ghosties strangers, weirdos, people with funny walk,or an IQ in the thousands i think these are distractions, we'd rather look at stories rather than reality

That’s Science Vs Serial Killers…

This Episode has been produced by Shruti Ravindran, Meryl Horn, Rose Rimler and me, Wendy Zukerman. Our senior producer is Kaitlyn Sawrey. We’re edited by Blythe Terrell. Additional editing help from Alex Blumberg. Fact Checking by Michelle Harris. Music by Bobby Lord and Emma Munger. Sound Design and mix by Emma Munger A big thanks to all of the other academics who helped us out, including Dr Mike Aamodt, Dr Ann Burgess, Dr Scott Lilienfeld, Dr Devon Polaschek, Dr Kori Ryan, Dr Kim Rossmo, Dr. David Finkelhor, Dr. David Keatley, Dr. Jennifer Lansford, Dr. Karen Franklin, Dr Michael Maltz, Dr Gabrielle Salfati, Dr Claire Ferguson, Dr Sandra Taylor, and Katherine Ramsland. Extra thanks to Sarah McVeigh, Christopher Suter [SOOTER], Frank Lopez, Rose Reid the Zukerman Family, and Joseph Lavelle Wilson . And everyone at Gimlet who listened and gave thoughts!

That’s it for this season of Science Vs! We will be back in the fall with some new episodes. If you want to suggest a topic for us to investigate - you can hit us up on Facebook. We’re Science Vs podcast there.  We’re also on Twitter at science v-s.

And just before we go, here are some of our favorite moments from this season … it’s been a lot of fun

END OF SEASON MASHUP

If you take away sex from a sex addict nothing happens, nobody ever died from blue balls

I woke up and could not move half my face

SETI institute freeze dried room, we have all the aliens you need

Just going to knock lots of things down.. It’s going to carry everything with it this hotdog stand that police car, swept away swept away. Dust everywhere. Nothing.

That’s a lot of willies… ahah yeah!

So if you like what you’re hearing - please tell your friends about us! And review us on iTunes… it really helps people more people find us.

I’m Wendy Zukerman… fact you soon!


[1]https://www.samhsa.gov/find-help/national-helpline 

[2] Edmund Kemper—intellectually brilliant, articulate, and lucid—shot his grandparents when he was 15 years old and then killed and mutilated eight women in California between May 7, 1972, and April 21, 1973

[3] After killing his grandparents, Edmund called his mother to inform her of his actions and then called the sheriff to confess.

[4]Madness, Deinstitutionalization & Murder-  California hospitalized him until he was twenty one, and then released him on parole in 1969.

[5] All Ed Kemper info from https://www.biography.com/people/edmund-kemper-403254 or EH book (which is in the SV office)

[6] according to Serial Murderers and their victims, by Eric Hickey, Kemper’s IQ was 136, P. 208

[7] he weighed around 300 pounds and was 6 feet 9 inches tall, which led to his nickname “Big Ed.” https://www.biography.com/people/edmund-kemper-403254 

[8] https://www.biography.com/people/edmund-kemper-403254; “However, when he offered a ride to two Fresno State students—Mary Ann Pesce and Anita Luchessa—they would never make it to their destination.... Kemper would later explain that he stabbed and strangled Pesce before stabbing Luchessa as well.” https://pdfs.semanticscholar.org/61ed/f43a32c5c78bef44a35a67b850cd092fd380.pdf

[9] http://maamodt.asp.radford.edu/Psyc%20405/serial%20killers/Kemper,%20Ed%20-%202004.doc

[10] May 7, 1972: “Edmund killed 2 students; Mary Anne Pesce and Anita Luchese from Fresno State College.  Placed Anita body in the trunk of his car and tried to strangle Mary Anne unsuccessfully.  Then stabbed her several times and cut her throat.  Ed removed Anita from the trunk and stabbed her with a larger knife.” http://maamodt.asp.radford.edu/Psyc%20405/serial%20killers/Kemper,%20Ed%20-%202004.doc  

[11] From EK description in youtube doc https://www.youtube.com/watch?v=tTnEY8y-p7M starting at min 5:10

[12] https://www.biography.com/people/edmund-kemper-403254 

[13] killed both his grandparents to "see what it felt like." Upon release, he drifted, picking up and releasing female hitchhikers. But he soon stopped letting them go, killing six young women in the Santa Cruz, California, area in the 1970s. In 1973 he killed his mother and her friend before turning himself in.” https://www.biography.com/people/edmund-kemper-403254 2+6+2=10  

[14] https://inmatelocator.cdcr.ca.gov/Details.aspx?ID=B52453

[15] Pg 5 http://maamodt.asp.radford.edu/Serial%20Killer%20Information%20Center/Serial%20Killer%20Statistics.pdf Radford University/Florida Gulf Coast University collaboration

[16] 371 + 117 http://maamodt.asp.radford.edu/Serial%20Killer%20Information%20Center/Serial%20Killer%20Statistics.pdf 

[17] Serial Murder: The unlawful killing of two or more victims by the same offender(s), in separate events.

[18] EMAIL: RR: “From this source it looks like the most recent definition of serial murder accepted by the FBI is "the unlawful killing of two or more victims by the same offender(s), in separate events." Is that correct?

Also, would it be correct to say: "A serial killer is defined by the FBI as someone who kills two or more victims but not all at once-- there was some kind of down time between the murders."

FBI press officer: “Yes, that is the current definition.”

[19] https://bond.edu.au/intl/profile/wayne-petherick

[20] https://sci-hub.tw/10.1002/bsl.742

[21] . There were ante-mortem sex (84.4%), the body left nude (76.7%), semen found at the scene (63.3%), sexual assault against the victim (52.2%), and vaginal sex (72.2%)

[22] https://sci-hub.tw/10.1002/bsl.742 (Table 4)

[23] Part of the difficulty for investigators is that the killer does not always leave unmistakable and unique signatures at his crime scenes.

[24] Twenty-six (70.3%) offenders also engaged in at least one of the uncommon, atypical behaviors listed in Table 2.

[25] Of the 37 offenders who engaged in ritualistic behavior, only 5 (13.5%) used exactly the same ritual with every victim in the series

[26] https://sci-hub.tw/10.1002/bsl.742

[27] . The results of the present study indicate that most serial killers are captured as a result of citizens and surviving victims contributing information that resulted in police investigations that led to an arrest. Those who were turned in by another person leading to their arrest. This category includes the largest portion of the sample population – 41 serial killers (20.5%).

[28] We asked teenagers at one UK school to list what they found to be morally disgusting; of several hundred examples the most common were rape, racism, killing, murder, torture, bullying, paedophilia, discrimination, necrophilia, genocide, exploitation, incest, theft, bestiality and cannibalism.

[29] among our patients was that of guilt around killing, injuring, or striking a defenseless

enemy.

[30] Worldwide: 41/41 (100%) of tabulated jurisdictions criminalize homicide.

[31] http://maamodt.asp.radford.edu/Psyc%20405/serial%20killers/Hall,%20Larry%20DeWayne.pdf 

[32] http://maamodt.asp.radford.edu/Psyc%20405/serial%20killers/Hall,%20Larry%20DeWayne.pdf 

[33] 34.5% of male serial killers sexually assaulted at least one of their murder victims.  Of course that doesn't mean that the motives for the other killers wasn't sexual, but they did not sexually assault their victims  [email]

[34] https://sci-hub.tw/10.1002/jip.27 They found sexual assault 61% of the time (table 1)

[35] https://sci-hub.tw/10.1002/bsl.742 Same group, later paper- found sexual assault 49% of the time (table 8)In table 5- vaginal sex happened 72.2% of the time

[36] Email : "Rape/lust typology: 65%. Anger was 10%.

[37] Along with manipulation, domination and control, a significant motivator for almost all serial killing is sexual, even if, as with Son of Sam David Berkowitz, the crimes themselves are not overtly so’’.. Blanchard (1995) agrees with this assessment stating that, ‘‘Male serial killers almost universally include a sexual assault as an integral part of their ritualized murder patterns’’ (p. 62).

[38] https://sci-hub.tw/10.1002/jip.118  Analyzed 19 serial killers. Out of  57 cases vaginal penetration occured 45.6% of the time, anal penetration occurred 17.5%, not sure if these are overlapping.

[39] From an italian study of 23 serial homicide perpetrators: Evidence of post-mortem sexual activity was rare (1.7%).

[40] rates on "post-mortem sex" from the paper https://sci-hub.tw/10.1002/bsl.742 Table 5: 15.6%

[41] Also study of >250 serial killers, see necrophilia and cannibalism,

[42] From the Aamodt database: One sample of 271 SK’s found 26 engaged in necrophilia = 9.5% http://maamodt.asp.radford.edu/Serial%20Killer%20Information%20Center/Serial%20Killer%20Statistics.pd f

[43] Clifford Olson, who raped and murdered eleven children in Vancouver, British Colombia, decided that the police “had the goods on him.”

[44] “Based on our latest numbers, the main broad motives for serial killers are: Financial Gain           30.1%”

[45] among female serial killers, killing for financial reasons may be the most common. http://sci-hub.tw/http://journals.sagepub.com/doi/abs/10.1177/104398629100700405 

[46] From FBI report, “In the Washington, D.C. area serial sniper case, John Allen Muhammad, a former U.S. Army Staff Sergeant, and Lee Boyd Malvo killed primarily for anger and thrill motivations. They were able to terrorize the greater Washington, D.C. metro area for three weeks, shooting 13 victims, killing 10 of them.” anger about racial injustice: http://articles.latimes.com/2003/dec/14/nation/na-snipers14 

[47] We have 5,014 serial killers in our database. Enjoyment  36.0% [Email] and see Study of 36 sexual serial killers from the FBI (page 48): mind states before the crime: 46% said hostility/anger, 50% said frustration, 41% said excitement, 43% said agitation and Survey of 57 African American + 205 Euro-American serial killers  found just under half did it for sex/hedonism: see Table 2

[48] Several days later, high school teacher Donald Harden and his wife, Bettye, were able to solve the cipher. "I like killing people because it is so much fun," it read. "It is more fun than killing wild game in the forest because man is the most dangerous animal of all."

[49] https://www.gresham.ac.uk/professors-and-speakers/professor-gwen-adshead/ 

[50] http://sci-hub.tw/https://www.bmj.com/content/348/bmj.g3643

[51] https://www.linkedin.com/in/gwen-adshead-b555ab21/ Two years as as Consultant Forensic Psychiatrist, and then as a Consultant in Forensic Psychotherapy for 15 years

[52] She has worked as a member of a therapeutic team whose role is to rehabilitate and offer secure psychiatric care to some of the most vilified and socially rejected members of society.

[53] https://www.gresham.ac.uk/professors-and-speakers/professor-gwen-adshead/ http://jaapl.org/content/41/1/38/tab-article-info about broadmoor: http://www.wlmht.nhs.uk/bm/broadmoor-hospital/ 

[54] Email, 2018, “We have IQ on 303 serial killers, the vast majority of them (281) are in the U.S.  It does not include the German serial killer study. The average IQ is 93.2 and the median is 85.0”

[55] The smart ones were a minority. Table 1: Only 5.4% had IQs above 120. 8.9% had IQs over 100.”. Hence, a serial murderer from the sample is slightly more likely to be of above average intelligence than someone who is randomly picked from the general population. “

[56] Earlier study by Mike Aamodt in 2007 on American serial killers, using data on the IQs of 95 serial killers (Aamodt et al., 2007), we find that the mean IQ is 103 and the median is 102—figures that place serial killers in the average range of intelligence.”

[57] From the table on intellectual capabilities measured by (IQ) tests, of the 56 serial killers sampled, the majority (42.9%) were just above average. 25% below average, 10.7% low.

[58] P. 125, Serial Murderers and their victims, https://books.google.com/books?id=Ob0KAAAAQBAJ&q=145#v=snippet&q=Kemper%20IQ&f=false 

[59] The media has created a number of fictional serial killer “geniuses”, who outsmart law enforcement at every turn. Like other populations, however, serial killers range in intelligence from borderline to above average levels.

[60] Eleven of the offenders (52.4 per cent) had some form of psychiatric diagnosis.” But doesn’t specify when the diagnosis was made

[61] According to the NCAVC, many serial killers are fully functioning adults who do not suffer from any outwardly apparent social or psychological disorders (Morton & Hilts, 2005).  

[62] P 320 “Of course, these clinical opinions result from post-hoc assessments. Hence it is not clear whether they are - at least in part - the causal factors or the outcoming of committing serial homicide.”  

[63]Psychiatric disorder prior to crime - Table 2 - About 18%

[64] The categorical system for diagnosing PDs in DSM-IV has been widely criticized on a number of grounds, including arbitrary symptom thresholds for diagnoses, low reliabilities for a number of the PDs, and high comorbidity among PDs

[65] From a study on German serial killers: “Salient aspects in the social behavior of these individuals, according to the clinicians (psychiatrists and psychologists) who assessed them for court proceedings, are the lack of orientation, a deficiency in forming and maintaining attachments or bonds to others, a lack of social impact, deficits in conflict competency, and a passive, at times hostile, basic emotional state paired with a lack of empathy”

[66] “Without the ability to ‘read’ other minds accurately, other group members may be identified as either ‘predator’ or ‘prey’, or (worse) something that oscillates between. There will be no opportunity to make attachment bonds to peers which allow groups to form that enhance safety and social function; lack of reflective function may result in social exclusion, which itself results in increased mortality and early death (House 1988)

[67] The authors, one of whom evaluated the subject shortly before her death, determined that she evidenced a psychopathic personality (PCL-R score 32).

[68] at least some sadistic killers may not require possession of an antisocial personality disorder to kill with moral impunity

[69] The most important finding of this meta-analysis is that the empathy differences between offenders and nonoffenders disappeared when SES was controlled for in the nonoffending and offending populations. Similarly, when intelligence was controlled the difference between offenders and nonoffenders disappeared in studies of sex offenders and was reduced in mixed offender studies.”

[70] The Pathways to Desistance study is a multi-site, longitudinal study of serious adolescent offenders as they transition from adolescence into early adulthood. Between November, 2000 and January, 2003, 1,354 adjudicated youths from the juvenile and adult court systems in Maricopa County (Phoenix), Arizona (N = 654) and Philadelphia County, Pennsylvania (N = 700) were enrolled into the study. Each study participant was followed for a period of seven years past enrollment with the end result a comprehensive picture of life changes in a wide array of areas over the course of this time.

[71] “We find that only 18 (1.33%) youth were charged with a homicide offense. Among the predictors, age, intelligence quotient (IQ), exposure to violence, perceptions of community disorder, and prevalence of gun carrying are significantly different across the two groups.” Amongst the 8 demographic characteristics and 35 risk factors they reviewed was the Psychopathy Checklist: Youth Version (PCL-YV) -- which includes measures of empathy, as well as Moral disengagement. “In this regard, these results may go ways to dispel some of the stereotypes about homicide perpetrators—that they are necessarily psychopaths or drug addicts who suffer from severe mental health illness—as none of these assumptions emerged in the Pathways study.”

[72]This paper doesn’t look at homicides specifically, but violence offenses Analyses of covariance indicated that individuals who had been physically abused in the first 5 years of life were at greater risk for being arrested as juveniles for violent, nonviolent, and status offenses. “Consistent with hypotheses, adolescents who had been physically abused in the first 5 years of life were more likely to have been arrested as a juvenile for violent and nonviolent offenses”

[73] “Abuse of all types excluding neglect was significantly higher in the serial killer population. For serial killers, the prevalence of physical abuse was 36%; sexual abuse was 26%; and psychological abuse was 50%. Neglect was equally prevalent in the serial killer (18%) and societal norm populations.

[74] https://sci-hub.tw/10.1177/0886260518759655 collected life histories from 25 SKs. They found a rate of abusive childhood in a study of 25 serial killers was 9/25 (=36%). They don’t have a control group, but in another paper, rate of child abuse in general population in were 11.8%.

[75] Killer physically abused -  44.0% Euro American, 16.7% African American

[76] P 319 Table 1 29-80% had “peculiarities in upbringings” Physical abuse was 47.3%   

[77] Edmund Emil Kemper III was born in Santa Cruz, California, in 1948. He was the unfortunate product of a broken and abusive home. At the age of 9, Edmund’s parents divorced, leaving him to live with his mother (Lane & Gregg, 1992; Martingale, 1993). She was very domineering toward Edmund. If he did not live up to her expectations, she would punish him in unusual ways. She would lock him in

the basement for long periods of time as a method of discipline

[78] No abuse (32%)

[79] It should be noted that there is a small number of serial killers who were raised in nonabusive, nonhumiliating, fairly nurturing families by their biological parents, and who had normal siblings. In my study, six men (Out of 99)

[80] https://sci-hub.tw/10.1177/0886260518759655 4/25 serial killers had “normal childhoods”, “Dennis Rader's young life seemed uncomplicated and happily ordinary to Roger Farthing, who grew up with him.” 

[81] Indeed in Jenkins's (1988) study, six out of 12 English serial killers had 'respectable' and superficially normal childhoods.

[82] https://www.census.gov/popclock/ 328,000,000 / 50 = 6,560,000

[83] Over half of female homicides for which circumstances were known were related to intimate partner violence (IPV).