Federal prosecutors have decided to drop the criminal case about how Heath Ledger obtained the powerful painkillers that contributed to his death.

The Drug Enforcement Administration (DEA) had blamed the painkillers oxycodone and hydrocodone found in Ledger's system were most likely obtained with phony prescriptions. But some other drugs, like sleeping pills or anti-anxiety medication were legally obtained with medical prescriptions.

But the prosecutors now dropped the case "because they don't believe there's a viable target." The federal agency's inquiry was expected to also involve Mary-Kate Olsen, whose lawyers claim that she had already told everything she knew about Heath Ledger’s last days and that she is not a drug consumer.

She also refused to talk to the Drug Enforcement Administration (DEA) without granted immunity."We have provided the government with relevant information including facts in the chronology of events surrounding Mr. Ledger's death," Michael C. Miller, Olsen’s lawyer said in a statement Monday when he also added " that Ms. Olsen does not know the source of the drugs Mr. Ledger consumed."

The woman who found Ledger’s body, Diana Wolozin, a masseuse, contacted Olsen in the first place, before even dialing 911. But apparently the actress hasn’t even confirmed that the conversation ever took place.

Heath Ledger’s body was discovered by his masseuse on Jan. 22. Olsen was a close friend of Ledger's. She was in California at the time she received the call but sent her personal security guards to the apartment to help.