Thirty-three years after the disappearance of Etan Patz, the only suspect ever arrested is as much an enigma as the missing child case that has baffled investigators for decades.
Unlike psychopaths, who show no remorse, Pedro Hernandez, a 51-year-old New Jersey builder, reportedly broke down emotionally during his confession. And unlike many molesters, Hernandez appeared to have no criminal record.
In addition, police offered no possible motive for the crime, saying only that Hernandez, then a teenaged stock clerk at a Manhattan bodega, confessed to luring the 6-year-old into the bodega for a soda and choking him to death in the basement.
Hernandez has told police he then stuffed Etan's body into a plastic bag that was thrown into trash elsewhere in the neighborhood. The body was never found.
He admitted to family members and friends as early as 1981 that he had "done a bad thing and killed a child in New York," according to NYPD Commissioner Ray Kelly. When confronted, Kelly added, the suspect confessed, expressing "remorse" and "relief."
Police said they had no reason to believe there were signs of sexual abuse, but homicide experts say authorities may be holding back.
"Hernandez certainly doesn't present as an organized killer," said Jack Levin, a professor of criminology from Northeastern University.
"It looks like his crime was spontaneous rather than methodically planned," he said. "Based on statistics concerning abductions by strangers and acquaintances, I would speculate that his motivation involved a sexual assault."
Despite stereotypes to the contrary, the recidivism rate among sexual predators is among the lowest, according to Levin.
"It is conceivable that Hernandez never again molested a youngster," he said. "This is particularly likely in light of his confession."
Feelings of remorse and empathy -- not typical in a sociopath -- might have kept Hernandez from repeating his behavior as he matured, he said.
The cold case was reopened in 2010 and, in April, investigators excavated a basement apartment steps away from Patz's home and the bodega where Hernandez said he killed the boy.
The new focus on the case led one of Hernandez's family members or a friend to alert police that they suspected Hernandez's involvement.
His neighbors in Maple Shade, N.J., said he led a quiet life and belonged to a Pentacostal Church, according to The New York Times.
Though Hernandez doesn't seem to fit the typical profile of a child killer, pegging a suspect into a psychological box can be misleading, according to according to Ken Lanning, a former special agent in the Behavioral Science Unit at the National Center for the Analysis of Violent Crime.
"It's complex, and no two cases are alike," said Lanning, who said he, too, doesn't know all the facts in the case. "But [police] must have a reason to believe his story."
Both Levin and Lanning warned about "false confessions."
"People come forward to confess because of publicity and notoriety," said Lanning. "Over the years, there have been two or three in-depth scenarios where someone claimed to be involved in the Etan Patz case."
For a decade, the prime suspect in the case was Jose A. Ramos, a former mental patient now imprisoned for molesting a boy in Pennsylvania. But he told police that he never killed the boy and put him on a subway.
"The police don't just believe people," said Lanning. "They must have some kind of standard to give this guy credibility. Most significant in a case like this is when a guy says, 'I can take you to the body.'"
But in Etan's case, police say it's "unlikely, very unlikely," that they would ever be found.
Hernandez reportedly told police he put the body in the trash, where it would have ended up in a city landfill.
"That can be a mess -- even a week later -- depending on the garbage and how it's compacted," said Lanning. "Especially 33 years later."
Child Abductors Don't Usually Kill
"When you look at these cases, 99 percent are released relatively unharmed," Lanning said. "Most people fall off their chairs when they hear that."
"Typically, they stop a child and lure them into a car, or the woods or backyard, or a basement and do something to the child -- sexual perhaps," he said. "Then, they let them go and the child is home before they knew they were missing."
But in cases of so-called "long-term" abductions such as that of Patz and Adam Walsh, who disappeared in a Florida shopping mall in 1981, "the outcome is not so good," Lanning said.
He added that investigators can't make assumptions based on other similar crimes.
"We don't have a huge number of these cases, and many are unknown," he said. "They have to consider all possibilities and they can't put all their eggs in one basket."
"The key here is consistency," said Lanning. "Is what he says he did consistent with what we know about him? If he says nothing went on sexually and then they find out this guy had been grooming and seducing 6-, 7-, 8-year-old boys, there's an inconsistency."
Police may holding back some of the details of the confession -- even hints of sexual molestation -- to spare Etan's parents, Stan and Julie Patz.
"They might not go into it, especially in a case this old," said Lanning. "Imagine the poor mother and father go through this 33 years later. He could have told them he did something with the boy and the police aren't saying it."
But investigators cannot rule out the possibility that Hernandez molested the boy, according to Lanning.
"It's easier for most of these guys to rationalize killing a child than having sex with a child," he said.
An FBI study of 500 children who were abducted and murdered found that about 75 percent of them had been killed within three hours of abduction. Some abductors kill for sadistic reasons, others for sexual gratification, but there are also those who kill because they "screwed up," according to Lanning.
"One of the least likely things a sexual predator will do is kidnap and murder his victims," he said. "A smart sexual predator doesn't kidnap anyone."
But sometimes things go wrong and the child "starts screaming and yelling and kicking and biting," said Lanning. "Now, he's got to stop the kid."
A certain number worry afterwards that if they release the child, they will tell, and so they go on to suffocate the child.
But all this is speculation, according to Lanning.
"What you think happened," he said, "is not so important as what you can prove happened."
On Friday, Hernandez was on a suicide watch at a New York City hospital just hours before he was arraigned on second-degree murder charges.
Russell Goldman and Richard Esposito contributed to this report.