YOU MENTION the words "serial killer" and the names of the damned flash before your eyes like glimpses of old nightmares.

Dahmer. Bundy. BTK. Heidnik. Graham. Gacy. The list goes on.

What they have in common - aside from an appalling ability to exterminate human beings with relative ease - is a tendency to eventually screw up and make sloppy mistakes that help put them behind bars forever.

That common flaw might be what helps Philadelphia police ultimately catch the Kensington Strangler - the maniac who has been linked through DNA evidence to the slayings of three women in the last month. So far, the killer has avoided capture despite a $37,000 reward, sketches and surveillance footage of a possible suspect.

"In many cases, the killer gets cocky. He feels omnipotent because the police haven't caught him," said Steven Egger, a prominent serial-killer expert and associate professor of criminology at the University of Houston-Clear Lake.

"He figures they won't catch him. Then he gets sloppy. Look what happened to Ted Bundy. He was caught running around in a stolen Volkswagen."

Egger speaks from experience. He worked decades ago as a homicide detective in Michigan. He was on the investigative team that arrested John Norman Collins, who murdered six women in southeastern Michigan between 1967 and '69.

Collins was spotted by a shop owner before he gave a ride to one of his victims. Hair found on her underwear linked Collins to the crime.

"Any serial-murderer investigation is difficult because you're talking about stranger-to-stranger homicides," Egger said. "In most instances, there aren't any witnesses. You don't have a whole lot to go on."

Philadelphia police have enlisted the help of the FBI to work up a profile of the Kensington Strangler.

Much of what investigators know about him has already been reported publicly. All of his victims - Elaine Goldberg, Nicole Piacentini and Casey Mahoney - were white women who battled drug problems.

All were found partially clothed and sexually assaulted in desolate Kensington lots known to attract prostitutes and drug addicts. Mahoney and Piacentini were positioned facedown, police have said.

"If he's posing the victims, it's a challenge to the police: 'Catch me,' " Eggers said. "I'm fairly sure he'll kill again because he's picking the most vulnerable people that he can find."

In that respect, the strangler shares something in common with Gary Heidnik and Harrison "Marty" Graham, two of Philadelphia's most notorious murderers.

Graham was convicted in 1988 of having strangled and raped seven women in his two-room North Philadelphia apartment. He kept his victims' remains in the apartment, and was caught only after he was evicted for the horrific odors that emanated from the rooms.

Heidnik kept five prostitutes as prisoners in his North Philadelphia basement between 1986 and '87. The women were regularly tortured and raped; two died.

Heidnik cooked the remains of one of the victims, Sarah Lindsay. Heidnik's house of horrors was exposed when he briefly let one of his captives, Josefina Rivera, go free. She called the police.

"Heidnik's slip-up was that he trusted [Rivera] too much," said attorney A. Charles Peruto Jr., who represented both Heidnik and Logan serial killer Juan Covington.

The strangler, he said, "isn't going trust anybody. He's a guy who's going to get himself caught from a mistake. A girl might get away, and a cop might be nearby."

Heidnik was motivated by "pure evil," Peruto said. The Kensington Strangler, he said, "probably gets a thrill from this. He does it, gets away with it, and gets attention in the newspapers."

Mark Safarik - a retired FBI profiler who testified at the trial of Robert Yates, of Spokane, Wash., who murdered 16 women between 1975 and 1988 - said the Kensington Strangler knows he can find easy prey along Kensington Avenue, where many women rely on prostitution to support their drug habits.

But with police and community members on high alert, striking again in Kensington could be too risky for the killer, Safarik noted.

"Someone is going to recognize this guy," he said, "unless he goes underground and leaves the area."

Staff writer Stephanie Farr contributed to this report.