NEW YORK (CBSNewYork/AP) — A man charged with killing a Manhattan boy who disappeared in 1979 calmly told investigators that he strangled the child, according to a confession video played in court Monday for a judge who will decide whether the recording can be used as trial evidence.

Pedro Hernandez has pleaded not guilty in the death of Etan Patz, who vanished on his way to school.

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In the video, Hernandez is sitting in a plain room with lots of chairs as a detective asks him about the child.

“I was nervous; my legs were jumping,” Hernandez replies. “I wanted to let go but I just couldn’t let go.”

“I felt like something just took over me. I don’t know what to say; something just took over me and I was just choking him.”

He demonstrated with his hands around his own neck. He said the boy was still alive when he put him in a bag.

Hernandez said he dumped the 6-year-old’s body and returned the next day, but it was gone.

Etan’s father watched stoically as the video was played, while the boy’s mother left the Manhattan courtroom before the video began.

Stanley Patz, the father of Etan Patz, attends a court hearing in Manhattan on Sept. 15, 2014. (credit: Juliet Papa/1010 WINS)

Stanley Patz, the father of Etan Patz, attends a court hearing in Manhattan on Sept. 15, 2014. (credit: Juliet Papa/1010 WINS)

Hernandez’s lawyer, Harvey Fishbein, says his client falsely confessed and lacks the mental ability to understand his rights.

Hernandez had been in custody nearly eight hours when the videotape was made, Fishbein said.

“We don’t have a record of what happened in that 7 1/2 hours,” he said. Hernandez asked to go home a number of times, Fishbein said.

Fishbein also said Hernandez got details incorrect that the killer should know, like where the body was dumped. “We will show he’s wrong all the time,” the defense lawyer said. “He’s unreliable. He’s a terrible historian; he’s inconsistent.”

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Assistant District Attorney Joan Illuzzi-Orbon told the judge that while Hernandez was questioned for hours before the video was made, most of it was very general about his life, WCBS 880’s Irene Cornell reported.

In 2012, police got a lead that brought them to Hernandez, who had worked at a bodega in SoHo where Etan disappeared.

After agreeing to go to a police station near his home in Maple Shade, New Jersey, he was questioned for about seven hours before detectives advised him of his so-called Miranda rights. They then recorded him saying he lured Etan into the store with a promise of a soda, suffocated him in the basement, put the body in a bag, stuffed the bag inside a box and left it on the street, authorities have said.

A judge will examine the timing of the Miranda warning, an often-disputed legal issue that turns partly on whether a suspect felt free to leave during any questioning before the warning. But the judge also will be asked to decide whether Hernandez made an “intelligent and voluntary waiver of his rights, and what role his psychological status and very low IQ play,” Fishbein said.

Hernandez has an IQ of 67, his medical records mention schizophrenia dating back years, and he’s taken anti-psychotic medication for some time, Fishbein said in papers filed in November 2012.

After his arrest, doctors diagnosed Hernandez with schizotypal personality disorder, an ailment characterized by “cognitive and perceptual distortions,” Fishbein wrote. A psychiatrist expert in determining the reliability of confessions found that relying on Hernandez’ statements would be “profoundly unsafe” unless there’s tangible corroborating evidence, according to Fishbein. So far, no such evidence has been found, he said.

The video was played Monday at the start of a hearing that will determine whether the confession can be used in court, not whether the statement itself is true. The hearing is expected to last several weeks.

Etan’s disappearance led to an intensive search and spawned a movement to publicize cases of missing children. His photo was among the first put on milk cartons and his case turned May 25 into National Missing Children’s Day.

Etan’s body has never been found.

His parents never moved or changed their phone number in case their son returned. In 2001, they obtained a court order officially declaring their son dead.

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