Secret Nirvana: The previously unseen artwork, journals and photographs of Kurt Cobain

ONE iconic song and a suicide. The two things Kurt Cobain is famous for make him seem like a one-dimensional poster boy for the grunge movement. But dig a little deeper and the reality is much more complex – and altogether more tragic.

Brought up in abject poverty, he is at once both little boy lost (witness his curvature of the spine, his ADHD for which he was prescribed Ritalin – and which he blames for his later drug abuse – and the lifelong irritable bowel syndrome that sparked an obsession with internal organs) and out-and-out weirdo, with a fascination for the ghoulish and macabre (he called his cat Spina Bifida, while a gift to one girlfriend was an LP with a naked Barbie doll tied to it and a noose around her neck).

Getting inside his head would be a challenge for anyone, but Charles R Cross felt up to the task. A longtime fan of Nirvana, the author had seen the band in their early days, charted their rise to superstardom and written Heavier Than Heaven, a biography of Cobain following his death in April 1994. During his research for that book, published in 2001, he came across a massive collection of artwork, journals and previously unseen photographs that gave an intimate and revealing insight into this most misunderstood of rock stars.

"One of the problems with writing a biography is that you can only fit in a limited number of pictures," he says. "So there was no way I could use the material I found in that book. And yet there was so much great stuff that Kurt created – the creative gene that made him a great musician was not just restricted to music."

The result is Cobain Unseen, part biography, part scrapbook, featuring hundreds of polaroids, drawings from the singer's childhood, items from his collection of kitsch Americana, as well as never-before-seen snapshots of Cobain with Courtney Love and their daughter Frances Bean. "One of the most amazing parts of the story is that there is a significant number of pictures that most people have never seen before, from rolls of film that had never been developed. So some of these pictures, when they say the word 'unseen', they mean it. Kurt Cobain took these pictures himself and even he never saw the finished product."

In one image, all that is visible of Cobain is his shoes, plus Frances Bean in a cot and a target practice poster on the wall. "The target practice was from the same shop where he bought the gun that he used to kill himself," says Cross. "So in that one picture, you have the joy of fatherhood, you have the target that he doctored with a K Records logo – so it was funny, it was sarcastic, it was tragic. To me, that's one of the images that sum him up."

Also included in the book is Love's personal favourite photograph, an image of Cobain on an iron bed in their Seattle home, taken in 1993. "It's so poignant, because he looks so sad," says Cross. "Courtney says it shows the private side of him."

For Cross, one of the most dramatic discoveries was a letter – or rather a furious diatribe – in which Cobain threatens to disband Nirvana. "It was harrowing. Of course I'd read about them breaking up, but actually to see a letter in his own handwriting – and the way it was written – made it clear how messed up he really was."

He admits that, at times, it was difficult for him to separate fact from myth and from his own fandom, "but at the same time it's almost like putting a puzzle together. The first biography was a small part, and this is another that helps build up the picture of what Kurt was like."

• Cobain Unseen, by Charles R Cross (Hodder, 30), is published on Thursday