The Lost Boys star passed away in Los Angeles last Wednesday (10Mar10). He was found unresponsive at his mother's house and later pronounced dead in hospital after suffering a suspected overdose.
Haim, 38, was open about his long battle with his addictions, but was believed to have sobered up over the last few years.
Now TV producer Jim Katz has revealed he worked with the late star on a reality TV show a year ago called Lost Boy Found, chronicling Haim's efforts to kick drugs.
He tells E! Online, "Corey was doing drugs, and everyone knows that. This project wasn't about exploiting him or showing him stoned. This was about his decision to clean himself up."
The show, which was never broadcast, also documented Haim's dream of pursuing a career in music - and his plans to hit the road with his musician pal Gerard 'G Tom Mac' McMahon, who worked on the Lost Boys soundtrack.
Katz adds, "What people don't know is that Corey actually had an amazing singing voice.
"He was a charming little kid. I call him a little kid, because he was like a sweet little kid with so much love."