By Natasja Sheriff

NEW YORK (Reuters) - The mother of a New York boy missing since 1979 took the witness stand in the trial of his accused murderer on Tuesday, telling the jury that she has avoided the courtroom out of fear the descriptions of the crime would leave her sleepless.

Pedro Hernandez, 54, is on trial for kidnapping and murder in a case that hinges on his confession to police in 2012 that he choked 6-year-old Etan Patz, stuffed him in a box and left him in a New York alley.

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.

Defense attorneys say Hernandez's confession was coerced by police. They say he is mentally ill, intellectually disabled and suffers from hallucinations.

In state Supreme Court in Manhattan, Julia Patz said she had avoided attending the trial except for her initial testimony on Feb. 2.

"I chose not to subject myself to hear the details of the alleged confessions," she said.

Patz said if she heard the disturbing details, they would be etched in her mind and leave her unable to sleep.

Prosecutors asked her about Jose Antonio Ramos, who defense attorneys say is the real killer. Ramos' girlfriend walked Etan Patz to school during a school bus strike, and for years Ramos was the prime suspect.

Ramos has said he had been inside the Patz family's apartment, according to investigators in the case, but the boy's mother disputed that claim.

He had never been in their home and his girlfriend was never left there alone babysitting, she said.

Ramos told investigators he sexually molested a young boy in 1979 who may have been Patz, according to trial testimony. Ramos has said that afterward he put the boy on a subway.

Patz has never been found, and he was declared dead in 2001.

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

Trial testimony is expected to conclude next week.

If convicted, Hernandez faces the possibility of life in prison. He has not testified at his trial.

(Reporting by Natasja Sheriff; Editing by Ellen Wulfhorst and Eric Beech)