From early on, GraBois believed that Ramos was involved in Etan's disappearance. Some boys had accused Ramos of trying to lure them inside a drainpipe, where he lived in 1982 in the Bronx. When police searched the drainpipe, they found photographs of Ramos and young boys who resembled Etan, but no charges were pressed and Ramos vanished. GraBois eventually found out that Ramos was in custody in Pennsylvania in connection with an unrelated child molestation case.
GraBois brought Ramos to New York to meet face-to-face. Ramos had no idea why he was there. Out of the blue, GraBois asked him directly, "How many times did you have sex with Etan Patz?" According to GraBois, Ramos "froze" and said, "I'll tell you everything."
Ramos' response is now known as "the 90 percent confession." He admitted taking a young boy back to his apartment for sex on the day Etan disappeared and told GraBois he was 90 percent sure it was the boy he later saw on TV. As GraBois pointed out, "the only boy missing and on television that evening was Etan Patz." GraBois said that at that moment he "believed we had the right guy."
But the confession was not complete. Ramos did not use Etan's name and he claimed he had "put the boy on a subway."
GraBois himself would never hear the last 10 percent of the story that he was after. However, during Ramos' time in lockup, two convicted criminals, claimed to have knowledge about Ramos and volunteered to try to get more information from Ramos about the Patz case.
One informant told GraBois and FBI agent Mary Galligan that Ramos told him that he knew what happened to Etan. Ramos had even drawn a map of Etan's school bus route, pointing out that he knew Etan's stop was the third one.
In an interview with 20/20 on the thirtieth anniversary of his son's disappearance, Stan Patz said each year he sends a special reminder to Ramos in prison that the case is not forgotten. He mails one of the old lost child posters to Ramos with a simple typewritten line on the back that reads: What did you do to my little boy?
ABC News' Emily Friedman contributed to this report.