Spike Lee has revealed he is close to finishing a Michael Jackson documentary marking the 25th anniversary of the singer’s Bad album.

The director said the footage to which he was given access was a “treasure chest of findings”.

“We have footage in this documentary that no one’s ever seen – stuff that Michael shot himself and behind the scenes stuff,” he said.

The film is due to be released later this year.

It tells the story behind the 1987 album, the record-breaking world tour it led to and the short film music videos it spawned.

These include the video promo for the title track, directed by Martin Scorsese and featuring the actor Wesley Snipes.

“We had complete access to the vaults of Michael Jackson,” Lee said. “He wrote 60 demos for the Bad record. Only 11 made it.

The documentary features 40 interviews Lee conducted with Jackson’s confidants, choreographers, musicians and other collaborators.

He also includes interviews with Kanye West, Mariah Carey and Sheryl Crow – who was a backup singer on the Bad tour – about the album’s lasting influence.

“We really divided it into two things,” Lee said. “Artists today who were influenced by Michael, and then people who worked side by side [with him].”

Besides Jackson’s artistry, Lee said the documentary would show a more personal side of the singer who died in 2009.

“He had a great sense of humour, and he was funny,” he said. “You’ll see a lot of that stuff.

“I’m more than just a huge fan of Michael Jackson. Having the chance to actually know him and work with him, I deeply care about his legacy.”

The 25th anniversary re-issue of Bad, titled Bad 25, will be released on 18 September.