The allegations that a churchgoing, married father of two was Kansas’ infamous BTK murderer have shaken the Hollywood image of the serial killer as disenfranchised loner. And it has people wondering just how many of their mild-mannered colleagues, spouses and fellow parishioners might secretly be monsters.

Estimates of how many serial killers are operating in the United States at any given time are, like the killers themselves, all over the map.

Jack Levin, who studies violence at Boston’s Northeastern University, estimates conservatively that there are about 20 serial killers operating nationwide, accounting for about 200 victims a year. Ann Rule, a true-crime author and serial killer expert from Seattle, figures there are about 300 such predators lurking “just below our level of awareness.”

A few years ago, the FBI — which defines a serial killer as someone who has killed three or more over a period of time — declared that the country was experiencing an epidemic of serial killings, and estimated that anywhere from 20 to 50 were prowling the country. But the bureau has since backed away from trying to quantify the threat.

“In the past we have had people here on our staff that have tried to make educated — or uneducated, guesses,” says FBI spokesman Ken Gross. He said the FBI’s headquarters offices were working with state and local officials on 16 cases they believe are connected to serial killers, but there may be others not involving the headquarters.

BTK case shatters myth

Last week’s arrest of Dennis Rader, a 59-year-old code enforcement officer and former Cub Scout troop leader, in the Wichita area’s “Bind, Torture, Kill” slayings is yet another blow to some commonly held myths about serial killers. Katherine Ramsland says the sooner people are disabused of such outdated notions, the safer they’ll be.

“There’s no single profile, despite what people are writing,” says Ramsland, a forensic psychology professor at Pennsylvania’s DeSales University who’s writing a history of serial killers.

Ramsland cringes when she hears that serial killers are most likely white and male, when she knows there have been plenty of black and female killers across history.

“They get perpetuated from one source to another,” she says. “That’s why someone like Dennis Rader can get away with what he’s doing, because these social stereotypes crop up. … We have cultural assumptions that they exploit.”

Brush with infamy

Every Tuesday and Sunday night, Rule sat beside a good-looking younger man, answering calls from people in crisis, people on the brink of suicide. The Victorian house where the hot line operated was in a tough Seattle neighborhood, so when they finished their shift at 4 a.m., the clean-cut young man would escort Rule to her car.

“He would say, ‘Please be careful. I don’t want anything to happen to you on the way home. And keep your doors locked,”‘ she recalls.

That man was Ted Bundy, who would one day confess to killing 28 young women, though he was suspected of slaying dozens more.

“If there was any danger in him, I never spotted any clue at all,” says Rule, a former police officer. “Mostly it’s because they wear a perfect mask, that the world sees. And that mask never slips until it’s too late, and the victims see it when they’re far away from any help.”

So why didn’t Bundy come after Rule? Because she was a 34-year-old, slightly chubby divorced mother of four with auburn hair, she says — not a slender coed with long dark hair parted in the middle.

“I was not his type.”

Hard to catch

While about half of all serial killers are caught within a year, Levin says many are hard to run down because of the victims they often choose: prostitutes and runaways who were strangers to the killer.

“What happens is the police typically have the dump site, but not the crime scene,” says Levin, who recently published “Extreme Killing: Understanding Serial and Mass Murder.” “And by the time they locate the body, they’re left with skeletal remains. They don’t have DNA, they don’t have fibers, they don’t have fingerprints.

“They’re lucky if they can identify the victim, let alone the killer.”

Because serial killers are individuals with their own histories and motives, it is very hard to talk of them generally, Ramsland says. One common trait, she says, is that they are psychopaths, who, brain scan studies show, fail to process “the emotional content of situations, such as empathy, concern or alarm.”

Technology vs. luck

Back when he coined the phrase “serial killer,” former FBI profiler Robert Ressler could safely say that most of his prey were single, white, unemployed males. And it seemed the United States had the market cornered.

Now, he travels the world, lecturing on black, Hispanic and Asian killers; on killers who target acquaintances, not just strangers; on married career guys like suspect Rader.

“These things emerge and change,” he says. “The old rules of the ’70s just don’t apply anymore.”

Profiling is rapidly giving way to the use of linked DNA and crime databases.

“Years ago, you solved the serial murder case strictly by luck,” Ressler says. “Today it’s by technology.”

BTK eluded capture for 30 years. But police say they lucked out when Rader left an electronic fingerprint: a floppy disk sent to a Wichita TV station by the BTK killer was traced back to Rader’s church.

Ressler is annoyed at complaints he’s read about how long it took to arrest someone in the BTK case. He says those people have no idea what they’re talking about.

“When you get a person that is a ghost, who is operating in an invisible status, it can take a long time.”