An autopsy to determine Philip Seymour Hoffman's cause of death has proved inconclusive. Coroners carried out a full examination of the tragic Capote star's body on Monday (03Feb14), a day after he was found dead from an apparent drug overdose at his New York City apartment (02Feb14). However, initial tests failed to pinpoint the exact reason for the actor's passing and officials at the city medical examiner's office are now expected to conduct further toxicology and tissue tests. Police allegedly discovered large quantities of heroin at Hoffman's rented home, with one witness telling investigators that the 46 year old had been spotted buying narcotics from two men on the eve of his passing. The actor spent time in rehab for substance abuse issues last year (13) after more than two decades of sobriety. Meanwhile, four people have been arrested, reportedly in connection with supplying the late star with drugs, following a raid on a Manhattan property on Tuesday night (04Feb14).