Mary-Kate Olsen is keeping her mouth shut (don't get too excited, though; this new policy doesn't seem to extend to her acting roles.) The trouble-attracting twin is seeking immunity before agreeing to participate in a federal investigation into Heath Ledger's death, reports the New York Post.

According to the Post, Olsen is the final witness the feds need to question before concluding their investigation into where Ledger got the drugs that led to his accidental overdose on Jan. 22 in New York City. Ledger's masseuse found his body and -- instead of calling 911 -- immediately called Olsen, who reportedly asked her bodyguards to race to the scene. Her security team arrived at Ledger's apartment the same time as the paramedics.

But Olsen is refusing to talk about that fateful day unless she receives immunity from prosecution, reports the Post. E! News is also confirming the report.

"Everyone has been very eager to help, saying what a great guy Heath Ledger was, everyone except Mary-Kate, who has refused to speak," a source tells the paper.

Regardless of the reports, Olsen's lawyer insists the pint-sized actress is co-operating with authorities.

"Despite tabloid speculation, Mary-Kate Olsen has nothing whatsoever to do with the drugs found in Heath Ledger's home or his body, and does not know where he obtained them," attorney Michael C. Miller said in a statement. "Regarding the government's investigation, at Ms. Olsen's request, we have provided the government with relevant information including facts in the chronology of events surrounding Mr. Ledger's death and the fact that Ms. Olsen does not know the source of the drugs Mr. Ledger consumed."

If Olsen is too terrified to tell her tale, perhaps she should send sister Ashley in her place? What's the point of having an identical twin if you can't pull a bait-and-switch to get out of awkward interrogations every once in a while?

© (c) CanWest MediaWorks Publications Inc.