By Natasja Sheriff

NEW YORK (Reuters) - An expert on false confessions testified on Thursday that a former grocery store worker accused of killing a missing New York City boy in 1979 could be at risk of falsely admitting to a crime due to mental illness and low intellectual abilities.

Pedro Hernandez, 54, on trial for the kidnapping and murder of 6-year-old Etan Patz, confessed to police in 2012 that he choked the boy, stuffed him in a garbage bag and box and left him in a New York alley.

Defense attorneys say Hernandez concocted a false confession under police coercion and that he suffers from mental illness and hallucinations. He could face life in prison if convicted.

Patz vanished as he walked alone for the first time to a school bus stop in his Manhattan neighborhood on May 25, 1979. His disappearance sparked a national movement to find missing children, with his picture one of the first to appear on milk cartons.

Dr. Bruce Frumkin, a forensic psychologist and expert in false confessions, testified in state Supreme Court in Manhattan that tests show Hernandez has an IQ of about 70, putting him in the lowest 1 to 2 percent of the population.

Hernandez is at risk of confessing falsely to a crime because intellectual disabilities and mental disorders can make people vulnerable to demands by police and to interrogation tactics, he testified.

Someone with such a low IQ "doesn't have the intellectual resources to assert themselves," he testified. "They tend to be more suggestible and believe things police say."

Frumkin and another psychiatrist who testified last week said Hernandez suffers from a schizotypal personality disorder, a mental illness that makes him unable to distinguish between hallucinations and reality.

Patz has not been found. He was declared dead in 2001.

Frumkin said he would not provide an opinion about whether Hernandez had made a false confession.

"It's for the jury to decide how much weight to give Mr. Hernandez' statements to law enforcement," he said.

Hernandez was questioned and arrested in 2012 after police got a tip that he had confessed to the crime to a church prayer group in New Jersey.

Hernandez's attorneys blame another man, Jose Antonio Ramos, who for many years was a prime suspect in the case. Ramos is a convicted child molester in prison in Pennsylvania.

(Editing by Ellen Wulfhorst; Editing by Mohammad Zargham)