Spike Lee working on a Michael Jackson documentary

(CBS/AP) Spike Lee has been combing through footage of his late friend Michael Jackson as he starts to work on a documentary about the singer's "Bad" album.

Lee calls his search a "treasure chest of findings."

"We have footage in this documentary that no one's ever seen, stuff that Michael shot himself, behind-the-scenes stuff," he said in an interview Monday. "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."

He added: "You don't have to be a Michael Jackson-head to enjoy this."

Lee's documentary will be part of a flood of material to celebrate the 25th anniversary of the "Bad" album, Jackson's follow-up to "Thriller" that included hits like the title track, "Smooth Criminal," "The Way You Make Me Feel" and more. The album is being rereleased Sept.18 with additional tracks, a DVD and other bonus material; Lee's film is due to come out later this year, but no date has been set.

Besides Jackson's artistry, Lee said the documentary will show a more personal side of the late legend.

"He had a great sense of humor, and he was funny -- so you'll see a lot of that stuff," he said.

Lee interviewed people ranging from Kanye West to Mariah Carey to Sheryl Crow, who was Jackson's background singer on the "Bad" tour.

"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.'"

Besides the documentary, Lee also plans to hold his now annual birthday tribute to Jackson in Brooklyn, N.Y, on Aug. 25; Jackson would have turned 54 this year.

"This year we're going to focus on the 'Bad' album, we're going to focus on the 25th anniversary, but at the same time we're going to play his full catalog, including the Jackson 5 and the Jacksons," he said. "It's going to be even bigger and better this year."