A crack pipe and prescription pills were found in DJ AM's New York City apartment, the Associated Press reports.
A law enforcement official, who spoke to the AP on condition of anonymity because the investigation was ongoing, did not release any other information about the medication.
Last year, the star -- who was found dead Friday at the age of 36 -- revealed that he became addicted to drugs and had attempted suicide in his early 20s. He said he attended recovery meetings and has remained drug-free for about a decade.
"He was sober for 10 years, a friend told Us. "His sobriety was really important to him."
He even began working on a new intervention-style reality show based on his experiences surviving addiction as well as surviving a tragic plane crash nearly a year ago that left four others dead.
"I have another chance," he had said during a July interview for the MTV show, Gone Too Far. "So I have to do something better with my life this time."
There was no evidence of foul play, and it has not yet been confirmed if DJ AM had drugs in his system when he died. The police source said a medical examiner will determine the cause of death.
"[His] death is an incredible loss to the music community, his friends, family and his fans, and to those of us who had the privilege of working with him," an MTV spokesperson said in a statement late Friday. "MTV was honored to support him as he helped young people battle their own addiction."