Police investigating the death of actor Philip Seymour Hoffman have found close to 50 envelopes of what they believe is heroin in his Manhattan apartment, two law enforcement sources familiar with the inquiry told CNN on Monday.

A number of used syringes, prescription drugs and empty bags that authorities suspect used to hold heroin also were found in the apartment where Hoffman, 46, was found dead Sunday of an apparent drug overdose on the bathroom floor with a syringe in his left arm, the sources said.

The New York medical examiner's office will conduct an autopsy Monday, according to law enforcement sources.