Forensic Psychologist: Accused Killer's Motivation Is Key To Understanding Patz Murder Mystery

NEW YORK (CBSNewYork) -- As the criminal case in the Etan Patz killing proceeds, prosecutors are tracing back Pedro Hernandez's whereabouts over the decades.

Many questions still remain after police said Hernandez confessed, including how he has lived with the alleged deadly secret for so many years.

Police Commissioner Ray Kelly didn't reveal Hernandez's motivations for the admitted killing of Etan Patz. However, Dr. N.G. Berrill, a forensic psychologist at John Jay College of Criminal Justice, said whatever the motivation was --- that is the key to understanding what happened 33 years ago.

"What would have motivated him to take the boy off the street and bring him into the basement of a bodega? Sex or sexual misconduct is the first thing that comes to mind," Berrill told CBS 2's Dick Brennan.

Berrill doesn't believe Hernandez is a thrill killer or serial murderer, but said he could be a pedophile.

"It would surprise me to know that he killed someone else, but would it surprise me that he had sex with other kids or preyed on other kids sexually? No," said Berrill.

Berrill said Hernandez's behavior suggests he may never have intended to kill Etan Patz.

"If this is a type of a person who really doesn't have a taste or desire to kill anyone, then this could have been an inadvertent act," said Berrill. "He might have been frightened that the boy was yelling or attracting attention. It's a different scenario than someone who purposely and specifically goes out hunting for children and enjoys killing people."

Because Hernandez confessed to killing Etan Patz and expressed remorse, Dr. Berrill suggested he may be mentally ill, but not a psychopath.

"If in fact he is guilty of this crime, it might have frightened him to the point where he kind of swore off involving himself in this kind of activity," Berrill said.

Why did Hernandez coming forward now?

There is information he has a medical condition -- his attorney claims Hernandez is bi-polar and schizophrenic and prone to hallucinations -- or perhaps he finally wanted to clear his conscience, experts said.

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