While actress Mary-Kate Olsen asked for immunity from prosecution before cooperating with the police in the case of Heath Ledger's sudden death in January, her lawyer insists she has no clue where the actor got the drugs that killed him, and has already provided investigators with "relevant information."

"Despite tabloid speculation, Mary-Kate Olsen had nothing whatsoever to do with the drugs found in Heath Ledger's home or his body, and she does not know where he obtained them," the starlet's attorney, Michael C. Miller, told People on Monday.

It was reported earlier that Mary-Kate Olsen, who refused to speak with the police about Heath Ledger's drug-fueled death, requested immunity before sharing any information with the police.

"The Dark Knight" star was found dead on January 22, from what was later identified as a prescription drug interaction. Six prescription medications were found in his system, none of which was taken to excess. He took a normal amount of two drugs for anxiety, two sleeping medications, and two pain medications.

At the time of his death, "The Dark Knight" star was suffering from pneumonia after filming in cold rainy London on late nights for "The Imaginarium of Dr. Parnassus," and had trouble sleeping after the anxiety and stress of playing The Joker in the Batman movie. He supposedly forgot about taking some of the pills and could inadvertently took more.

Investigators from the US Drug Enforcement Administration looking into how Ledger obtained the drugs concluded that he had legal prescriptions from two doctors for all medications but one of them. OxyContin.

They conducted interviews with everyone close to the actor, including his doctors, the masseuse, bodyguards, housekeepers, business associates and even the mother of his 2-year-old daughter, Matilda, his "Brokeback Mountain" co-star Michelle Williams, except Mary-Kate Olsen, who was the first person whom the masseuse, who found Ledger unresponsive in his New York apartment, called.

"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 was quoted by the New York Post as saying.

Before the emergency services were summoned, she had called Mary Kate Olsen, also a client of hers, twice. The actress sent two private security guards to Ledger's apartment but failed to tell the masseuse to call 911.

While the New York Police Department already closed the case, federal officials are still interested. They contacted her lawyer several times recently seeking her cooperation, but Miller told the feds Olsen will not be interviewed unless she gets immunity, exercising her constitutional rights. Feds are trying to identify where the actor got the OxyContin.

"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," the statement from Olsen's attorney added, concluding that Olsen is unaware of the sources of information quoted in the media, dismissing them as "incomplete and inaccurate."