It was big day of testimony Monday in the Etan Patz murder case with an effort by the defense to suggest that someone else killed the six-year-old boy in 1979. NY1's Michael Herzenberg filed this report.

Former Federal Prosecutor Stuart GraBois took the stand Monday on behalf of accused murderer Pedro Hernandez.

As an assistant U.S. attorney, Grabois spent years investigating whether someone else killed Etan Patz.

He testified Monday that another man, Jose Ramos, told him he was 90 percent sure he lured Etan Patz to his apartment the day the six year old disappeared in SoHo. 

Ramos said he tried to abuse the boy, but the boy resisted, so he put him on the subway.

"How many times did you have sex with Etan Patz?" Grabois said he asked Ramos.

"He froze," GraBois testified. "Then he said, 'I'll tell you all about it. I want to get it off my chest.' "

Ramos never did tell all though. He immediately lawyered up. 

The ex-prosecutor's testimony is a centerpiece of the defense's case. by suggesting that someone else might have killed little Etan.

"The burden that the defense has is so much less than the burden the prosecution has, so if they can introduce reasonable doubt because there's another suspect with some viable evidence, that's there burden and it puts things in a very different light," says Lisa Cohen, author of  "After Etan: The Missing Child Case that Held America Captive."

Ramos has always denied killing Etan. 

In a 1982 interview with Bronx prosecutors—four years before his interview with Grabois—he said of Etan: "I never saw Etan. I never met him,"

Police had picked up Ramos up for allegedly trying to pick up two young boys.

Under questioning he admitted then that his girlfriend walked Etan home from school, a key connection.

"Susan used to take care of him. Susan Harrington," Ramos said in the 1982 interview.  

Ramos has served 20 years in prison for molesting other children. In his 70s, he's still locked up.

Prosecutors felt they couldn't find enough evidence to charge him with Etan's disappearance.

Etan's parents later sued Ramos for wrongful death, and in 2004, they were awarded a $2 million default judgment.

More evidence implicating Jose Ramos is expected in the coming days. Jailhouse informants inserted into Ramos' cell are expected to testify he revealed details about what he did to Etan all those years ago.