US actress Mary-Kate Olsen has refused to talk to officers investigating the death of Heath Ledger unless she is granted immunity from prosecution.
Officers want to talk to Mary-Kate Olsen
The 22-year-old was a friend of the actor and the first person called by his masseuse who found the 28-year-old dead in his apartment.
Ledger died from an accidental prescription drug overdose in his New York home in January.
The actress called private security guards to the actor's house at the same time as emergency services
A source has said Olsen, best known for her role in the TV series Full House, won't co-operate with federal investigators without the immunity.
The US Drug Enforcement Administration is investigating where the Batman star got his drugs and medicines.
A source said: "We have asked to interview her twice and it has not happened."
Negotiations are said to be on-going between the unit, Mary-Kate's lawyers and the prosecutor's office.
Olsen's lawyer Michael Miller said he had provided officers with relevant information, including a chronology of the event surrounding the death.
He said: "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."
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Heath Ledger as the Joker in the latest Batman movie
Heath Ledger was nominated for an Oscar for his role as a gay cowboy in 2005's Brokeback Mountain.
His final role as the Joker in the recently released Batman sequel The Dark Knight, is being touted as winning him an Oscar in 2009.
The actor leaves behind a two-year-old daughter, Matilda, with his Brokeback Mountain co-star Michelle Williams.