mary-kate olsenMary-Kate Olsen reportedly will be forced to testify in the investigation into Heath Ledger’s death if she doesn’t submit willingly to questioning.

While denying any knowledge of the drugs that killed Heath in January, the actress is said to have demanded immunity from prosecution if she talks to the investigators about the case - but now a spokesperson for the Drug Enforcement Administration in New York has confirmed that they’ve issued a subpoena that will force Mary-Kate to testify in front of a grand jury.

Investigators have tracked down prescriptions for nearly all of the drugs found in Heath’s body and apartment at the time of his death but are still trying to establish how he acquired Oxycontin and Vicodin without a prescription. They have spoken to almost everyone involved with the death - from Heath’s former fiancee Michelle Williams to the masseuse who found his body - but have yet to speak to Mary-Kate.

A legal source, not associated with the case, told Access Hollywood that the twin’s request for immunity should not be construed as admitting guilt: “It may not mean anything other than she’s getting good legal advice.

“You don’t know what the DEA may suspect in this case and I think it’s a cautious way to proceed. I think it would be wrong to assume she’s done something criminal simply because she’s invoking her 5th amendment against self-incrimination.”

Mary-Kate was linked to the actor shortly before his death and on finding his body, the masseuse repeatedly called Mary-Kate before calling the emergency services. Mary-Kate’s medically trained bodyguard reached the apartment at the same time as the paramedics.