Heath Ledger heathmk.jpg Looks like the paps aren't the only ones to receive the silent treatment from Mary-Kate Olsen - the New York Post reports that the Full House actress has refused to be interviewed about her friend Heath Ledger's death!

Not Talking To Cops
The Post claims that Mary-Kate's lawyer has repeatedly fended off the feds seeking to interview the pint-sized actress about Ledger's behavior, possible drug abuse, and the events immediately leading up to his death in January.

Police have been avidly pursuing an interview with Olsen ever since word got out that Heath's masseuse - the first person to discover the actor's body on the scene - called Mary-Kate before contacting the authorities.

Could M-K ID OCs?
According to the Post, the Drug Enforcement Agency thinks Olsen might be able to shed some light on a quantity of OxyContin - a powerful painkiller - found on the scene of Ledger's death.

Numerous drugs were found in Ledger's system and around his apartment, but all were legally obtained through two physicians - except for the Oxys.

The Post says investigators "are trying to ID the source of the OxyContin," according to a source. "Did it come from a dealer, from a friend? If he had a bottle from a friend, was it taken by someone else before police responded? That is what is trying to be determined."

Not Without Immunity?
The Post also alleges that Olsen might be willing to speak to authorities - if they can grant her immunity from prosecution.

Mike Miller, Olsen's lawyer, told the DEA that unless his client were guaranteed immunity, she would exercise her constitutional right and plead the Fifth.

When reached for comment by the Post, Miller would only say "We are not going to comment on whether there is a criminal investigation".

We sure hope Mary-Kate opens up to the cops soon - this sad story deserves a full explanation!