Philip Seymour Hoffman reportedly kept secret diaries that give an insight into the actor's struggle with drug addiction.
The Oscar-winner died of an apparent heroin overdose in New York last Sunday. He was 46.
NBC News reports the troubled actor penned entries into a journal about attending Narcotics Anonymous meetings in effort to stay clean.
Police apparently found two of the journals in the actor's apartment.
Sources tell the outlet some of Hoffman's most recent entries were made during his stint in rehab last May.
An insider reportedly familiar with the content spoke about the actor's sometimes incoherent thoughts.
"It's stream of consciousness and difficult to follow. In one line he refers to 'Frank who always owes money' and on the same page he writes about a 15-year-old girl from Texas," the source said.
"It seems he did at least part of it in rehab. It definitely contained some soul-searching. But there is also a fair amount of rambling that doesn't make sense," another insider added.
Hoffman was mourned last week during a funeral at the Church of St Ignatius Loyola on the Upper East Side of Manhattan.
Four hundred people attended, including Australian actress Cate Blanchett, Michelle Williams, Laura Linney, Julianne Moore, Michelle Williams and Amy Adams.
Hoffman's partner of 15 years, Mimi O'Donnell, and their three children Colin, 11, Tallulah, seven, and Willa, five, were also present.
The actor had been sober for 23 years when he checked into rehab last year after a relapse. It's unknown when he started taking drugs again but he did attend an Alcoholics Anonymous meeting on January 26, according to one attendee.
Three people have been arrested in connection with the actor's death.
Robert Vineberg has pleaded not guilty to a charge of heroin possession with an intent to sell.
Max Rosenblum and Juliana Luchkiw have also pleaded not guilty to charges of cocaine possession.
