Mary-Kate Olsen: Subpoenaed!

Note to celebrities: Do not stonewall the Feds.

Despite her claim that she has no information that would help clear up the mystery of Heath Ledger's overdose death, Mary-Kate Olsen has been issued a subpoena by the Drug Enforcement Administration office in New York.

The DEA order requires her to testify in front of a grand jury.

In a statement issued Monday, Mary-Kate Olsen's lawyer said that the frail actress had nothing to do with the drugs that killed Heath Ledger and that she has already cooperated with police in the investigation.

Celebrity news media outlets also reported that Mary-Kate Olsen refused to speak to investigators unless she was granted immunity from prosecution.

Access Hollywood broke the news about the subpoena on Tuesday night. No timeline has been given Mary-Kate Olsen might be called to testify.

Five different medications were found in Ledger's body at the time of his death, three of which he'd gotten from doctors in Texas and Los Angeles.

Officials are trying to determine how the late actor had the OxyContin and Vicodin found in his apartment without a legal prescription.

Olsen was the first person Ledger's housekeeper called after his masseuse found the actor dead from an accidental overdose January 22.