Spike Lee Finishing Michael Jackson Documentary

Movie focuses on the singer's 'Bad' album.

Director Spike Lee is finishing work on an upcoming documentary about Michael Jackson's landmark 1987 Bad album that will give fans a behind-the-scenes look at the Thriller follow-up that has sold more than 30 million copies worldwide.

Lee, who was friends with the late pop king and directed the official video for the posthumous single "This Is It,"
, said he learned a lot about MJ while making the as-yet-untitled movie.

According to the Hollywood Reporter, the movie will be part of a celebration of the 25th anniversary of Bad. "We have footage in this documentary that no one's ever seen, stuff that Michael shot himself, behind-the-scenes stuff," Lee said. "We had complete access to the vaults of Michael Jackson. ... He wrote 60 demos for the Bad record. Only 11 made it. So we got to hear a lot of that stuff, too, so it was just a great experience ... You don't have to be a Michael Jackson-head to enjoy this."

Bad, which was released more than five years after Jackson's breakthrough, Thriller, the best-selling album of all time, is also one of the all-time top-sellers. In a record tied by Katy Perry last year, it spawned five Hot 100 #1 singles, including "I Just Can't Stop Loving You," "Bad," "The Way You Make Me Feel," "Man in the Mirror" and "Dirty Diana."

The 25th anniversary re-release of Bad will hit shelves on September 18 and feature additional tracks, a DVD and other material. No release date has been announced yet for Lee's documentary, though it is slated to hit screens this year.

Lee sat down with everyone from Kanye West to Mariah Carey and Sheryl Crow (who was a back-up singer on the Bad tour) for the film, which he said will show fans a more personal, funny side of MJ. "We really divided it into two things: Artists today who were influenced by Michael, and then people who worked side by side - musicians, songwriters, technicians, engineers, people at the label, who were all committed to Michael, to the follow-up to the biggest record of all time, which still is Thriller," he said.

A doc chronicling Jackson's rehearsals for what was to be his series of comeback shows, "This Is It,"
 was released in 2009 and became one of the highest-grossing music docs of all time.