When Robert Ressler learned of Dennis Rader's description of how he bound and strangled people while acting out a sexual fantasy, it reminded him of another serial killer: Jeffrey Dahmer.
Like Dahmer, Rader masturbated at crime scenes, posed bodies and took pictures of his victims.
Ressler is a former FBI serial-killer profiler who later consulted with Dahmer's lawyer and wrote a textbook about the underlying motives of serial killers, called "Sexual Homicide: Patterns and Motives."
One thing Ressler has concluded about Rader and others like him who violently act out fantasies: "There's no way in the world... this guy would have a normal relationship."
The violence becomes a substitute for a healthy sexual or intimate relationship, he said. The abnormal sexual fantasy traces to experiences in pre-adolescence.
Tony Ruark, a Wichita psychologist who consulted with police on the BTK case years ago, said: "I've always been so curious as to what the devil happened in this guy's formative years."
Ruark said he hopes there is an in-depth psychological investigation of Rader and that it is made public.
According to Ressler, a serial killer's sexual fixation can be fed partly through hard-core pornography.
The future killer begins with window-peeping, obscene phone calls and less serious crimes, generally during his teens or early 20s, Ressler said.
"They build up. They don't start with murder," he said.
When the fantasy twists into a violent reality, it can be disappointing for the criminal, he added.
"I've had a number of these guys tell me that the acts are never as good as the fantasies," Ressler said.
Rader tied up his victims and usually strangled them. He told District Judge Greg Waller that he sought sexual pleasure through his actions.
Another thing that stood out was Rader's seemingly cold, detached description. He talked about victims going "down," as if they were animals.
In the serial killer's mind, Ressler said, "you take the life... for your momentary thrills. That's part of the serial murder process, is dehumanizing people." Such killers show no emotion because "they don't have that capacity."
Ressler also questioned whether someone like Rader can be counted on to be completely truthful. "I hope the judge realizes that these people are manipulators.
"They'll interject truth with their lies."
A remaining question is whether Rader killed before or after the killings he admitted to. Some serial killers, like Dahmer, start murdering in their teens. Usually serial killers start killing in their mid-20s.
Rader was 28 when he strangled the Oteros in their home on Jan. 15, 1974. He was 45 when he killed Dolores Davis in January 1991.
So it's possible that Rader started killing before the Otero murders, Ressler said.
Steve Osburn, Rader's chief public defender, said, "We have no reason to believe that there's any more (victims) out there."
Based on the serial-killer pattern, Ressler said, it's possible the BTK crimes could have stopped in 1991 with Davis' death, when Rader was 45.
Eventually, the drive to carry out the fantasy diminishes. Ressler calls it "psychopathic burnout." It comes when a killer reaches his late 40s or 50s.
It makes sense to Ressler that Rader started communicating with the media. The communication was the first from the killer in 25 years. It could be that Rader needed a boost, Ressler said. Serial killers "have very fragile egos."
The media attention is intoxicating, Ressler said.
"He's in the spotlight now. He's basking in it.
"A normal person would say: 'Who would want that kind of fame?' "