If serial killers are still considered an American phenomenon, it's because the US produces so many of them.
Two admitted to their crimes on Monday: "BTK" serial killer Dennis Rader who described in grisly detail how he strangled, stabbed and shot 10 victims to satisfy his sexual fantasies and Charles Cullen, a former nurse who killed as many as 40 patients in New Jersey and Pennsylvania.
Cullen on Monday also admitted to a further five murders.
These two men have joined a growing list of notorious killers who have sent chills through the nation and provided ample fodder for filmmakers and novelists.
From 1900 to 1999, at least 236 serial killers haunted the US, killing 3,130 people, according to Steven Egger, a police officer turned professor who has written extensively on the topic.
And it has been estimated that anywhere from 10 to 500 serial killers are active in the US at any given time.
"There are more serial killers among us than we know. When you start counting serial killers you're counting the ones we've caught," said Tomas Guillen, a professor at Seattle University and author of The Search for the Green River Killer.
When serial killers are finally caught it is often a shock to those who know them. Unlike the monsters and recluses of the movies, many serial killers are relatively personable, despite their sometime obsession with sex and death.
That's one reason why they are able to evade police.
"They're very, very smart -- not intellectually, but very, very streetwise," Guillen said. "They're very good at disarming people, especially women and children."
Serial killers are also able to evade detection because of the very nature of their crimes. Because they rarely know their victims they don't fall in the traditional circle of murder suspects. And they rarely leave behind evidence that links them to their victims.
DNA analysis is changing that.
Police had long suspected Gary Leon Ridgway of the Green River murders that terrified Seattle in the 1980s.
It was not until they compared a swab of his saliva to evidence found on his victims that police were able to charge him in 2001 with 48 murders.
The truck-driving Ridgway did not have the charms of another notorious US serial killer.
Ted Bundy was a handsome, charming former Boy Scout who admitted to killing 30 women but is believed to have slaughtered at least 100 during the 1970s.
A serial killer's death toll does not always measure their notoriety. David Falco Berkowitz, known as the "Son of Sam," killed just six people in the mid-1970s, but his letters to local media in New York City made him an apt character for a recent Spike Lee film.
Ed Gein, who inspired the films Psycho, Texas Chainsaw Massacre and The Silence of the Lambs, has only been linked to two murders.
It was what police found when they arrived at his dilapidated farmhouse in Wisconsin in 1957 that made him famous: bedposts made of severed heads, lampshades and chairs made of human skin, a necklace of human lips and an entire wardrobe made of human skin that he would wear while dancing in the moonlight.
Gein told police that most of his creations were made from the bodies of middle-aged women he dug out of a nearby grave yard.
Jeffrey Dahmer is perhaps one of the more gruesome modern serial killers.
A necrophiliac and cannibal who killed 17 mostly African-American men between 1978 and 1991, Dahmer kept several of the bodies of his victims in acid vats in his apartment.
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