heath ledgerThe investigation into the death of Heath Ledger has reportedly been closed by the New York Drugs Enforcement Administration.

The US agency was investigating how the Dark Knight star managed to acquire the drugs on which he accidentally overdosed in January. Prescriptions were tracked down for most of the narcotics but at the start of this week, there were said to be outstanding questions about the source of his Vicodin and OxyContin.

Investigators are said to have interviewed everyone remotely connected with the case - from his close friends and former fiancee Michelle Williams, to security staff and the masseuse who found his body - with just Mary-Kate Olsen resisting questioning until she was granted immunity from prosecution.

However, now sources inside the government authority have claimed the investigation has been closed by the US Attorney’s Office because they felt there was no evidence of criminal activity and there is no point pursuing the matter further “because they don’t believe there’s a viable target.

“There was no impropriety on the part of the doctors, they had actually examined [Ledger] and legitimately written the prescriptions.”