NEW YORK â€"  Pedro Hernandez provided detectives with "intimate details" about the murder of Etan Patz that only the killer could have known, sources said.

NYPD detectives believe these key clues, kept secret for 33 years, are proof that the former SoHo bodega stockboy charged in the infamous abduction knew too much to not be involved.

Sources said investigators were stunned to learn that Hernandez, 51, had this inside information, which cops never disclosed to the public despite intense public scrutiny and three decades of frustration in trying to unravel what happened to the six-year-old in 1979.

The specifics have remained secret and are known by fewer than a dozen current law enforcement officials, including Police Commissioner Ray Kelly and Manhattan District Attorney Cy Vance, the sources said.

They said the closely-held details likely relate to Etan's body -- scars, birth marks, moles or other identifying characteristics -- items he wore or had when he disappeared or knowledge the killer gleaned about Etan's family before the killing.

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