TORONTO -- The FBI has confirmed that 79-year-old Samuel Little, who has claimed to have killed more than 90 women between 1970 and 2005, is the deadliest serial killer in U.S. history.

Police have managed to match Little to 50 murder cases thus far, but they believe his other confessions are credible. Little has been serving a life sentence in prison since 2012 for the murders of three women.

“Someone like Little…he’s able to find a ‘target rich’ environment, in his case women who were living on the edge of society,” said Clint Van Zandt, a former FBI criminal profiler on CTV News Channel Tuesday.

Van Zandt said that serial killers, like Little, have the “uncanny ability” to find vulnerable victims, who may be poor or drug users or sex workers -- people who might not be missed right away if they go missing, “their absences are understood as a part of their life.”

His choice of victim is part of why he was able to be active for so long, said Van Zandt.

“Little says when you ask him, ‘How did you get away with this?’ he says ‘I just moved on to the next town,’” Van Zandt said.

One of the surprising aspects of this case is Little’s ability to recall what his victims looked like, an amount of recall that is “unusual,” Van Zandt said.

“When he [Little] starts to talk about the women that he has murdered, his eyes start to roll back and it’s like he’s got a set of old 35mm cassettes in his head and he’s just clicking through the pictures of each one of his victims… he’s got an amazing memory,” Van Zandt said.

Other serial killers will take a “trophy” from their victims, like jewelry or a shoe, to help them recall the “time they had with the victim,” Van Zandt said, but in Little’s case he can sketch his victims from memory alone.

Van Zandt said that Little was finally caught after police matched DNA on two or three victims and concluded they were probably killed by the same person – a database matched that DNA to Little.

A review by the FBI’s Violent Criminal Apprehension Program (ViCAP) then pieced together a pattern of “10, 30, 50, 90 similar murders” with Little’s modus operandi, Van Zandt said.

Van Zandt said that statistics suggest in the U.S. alone there have been more than 2,000 serial killers and that “25 to 50” are operating at any one time.