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Charlie Sheen's former assistant -- the man many claim was behind Charlie's drug binge last year -- was found dead, and TMZ has learned cops found a pharmacy full of drugs.

Rick Calamaro, who was in and out of Charlie's life for years, was found dead in his L.A. apartment yesterday, although it appears he was dead for several days.

Law enforcement sources tell us ... cops found "numerous pain medications and an open bottle of alcohol."

Rick was a club promoter who knew Charlie decades ago and some believe he supplied Sheen with drugs over the years.

Rick -- whom many Charlie insiders blamed for the actor's craziness in 2011 -- was with Charlie on the trip where Charlie trashed his room at The Plaza Hotel during a dispute with Capri Anderson.