The Green River Killer (search) provided a frank and articulate look into the mind of a serial killer.

His confession to 48 murders -- "Choking is what I did and I was pretty good at it" -- shows an unusual amount of self-insight, criminologists say. He knew what he was doing and on some level why he was doing it. He was deliberate in how he selected his victims and how he tried to throw off investigators.

But in most things but scale, Gary Ridgway (search) was not unusual for a serial killer, and his case and confessions contribute little new to efforts to understand what makes a serial killer tick.

"He's quite typical of prolific serial killers: He targeted strangers, he victimized prostitutes, he used dump sites," says Jack Levin, director of the Brudnick Center on Violence at Northeastern University.

It's the number of his victims and the two decades he avoided arrest that make Ridgway "the cream of the crop," Levin said. He was simply more careful about concealing his crimes and better about keeping his mouth shut than other serial killers of his type.

Ridgway pleaded guilty Wednesday in a deal that guarantees him life in prison without parole, rather than execution, for the 48 killings, most of them committed during a frenzied binge from 1982 to '84. His first victims turned up in or near the Green River in King County south of Seattle.

However, the plea bargain does not protect Ridgway from the death penalty in other jurisdictions. He has not been charged elsewhere, but admitted dumping victims outside King County and in Oregon.

His confession, read aloud in court by a prosecutor, was stunning in its frankness.

"I killed so many women I have a hard time keeping them straight," Ridgway wrote. "I picked prostitutes because I thought I could kill as many of them as I wanted without getting caught."

Even more disturbing elements came out in some of his statements: He returned to the sites to have sex with the corpses. He considered killing his "career." He was sexually attracted to his mother.

Still, those who study serial killers (search) say his admissions simply further confirm what they already knew: Serial killers tend to thrive on exercising control over their victims and over police, many hate women and target prostitutes because they're less likely to be reported missing, and they return to the places where they left the bodies unless they're likely to get caught.

The case also lends credence to the notion that while serial killers may be able to curtail their addiction when police are watching, they're extremely unlikely to kick the habit for good.

"He confirms a lot of the stuff we already know," said Robert Keppel, who investigated the Green River killings and questioned another serial killer, Ted Bundy. "He's talking about the things I would have expected him to have done. My main question is, is this it?"

The killings seemed to stop in 1984, after Marie Malvar's boyfriend saw her getting into Ridgway's truck and Ridgway became a suspect. Ridgway was questioned by detectives that year but passed a polygraph.

It turns out, however, that he killed again in 1986, 1990 and 1998.

"I don't think for a minute that he just stopped. He was addicted," says Mike Rustigan, a criminology professor at San Francisco State University.

Keppel agreed that Ridgway likely continued killing, possibly in other counties, except for pauses when detectives got close.

Ridgway, 54, told investigators he murdered more than 60 women in King County, and that the killing continued until 2001, when advances in DNA technology linked him to three of the deaths. King County prosecutors charged him with only those murders they could verify.

If there's anything unusual about Ridgway from a serial killing perspective, it's that he clearly articulated his thinking to investigators, that he held one job painting trucks for 32 years, and that he married.

Such stability is rare in serial killers, though not unheard of. Cannibal Jeffrey Dahmer held a job at a chocolate factory. Robert Yates of Spokane, who also preyed on prostitutes, had five children, a wife and a mortgage. William Lester Suff, convicted of killing 19 prostitutes in Riverside County, Calif., worked as a stock clerk for the county for nearly a decade before his arrest.

While criminologists have been able to categorize their behavior to some degree, they say they've had no luck answering the toughest question: What makes a serial killer?

"It is true that most have had terrible childhood experiences, and that some have been abused, abandoned or sexually stimulated by a parent," Levin said. "But here's the problem: There are millions of healthy, decent humans beings who suffered as children, and they don't kill anyone. So that's an incomplete explanation.

"We've been studying this for maybe 25 years, and we're still in the dark in understanding where it comes from."