We're standing with Brant, a 27-year-old Nirvana fan, next to the graffiti-peppered bench, pock marked with poems and knife tributes (I LOVE U KURT ALWAYS, ALL APOLOGIES SARA X etc) outside Kurt Cobain's mansion on the shore of Lake Washington (right next door to the CEO of Starbucks' mansion).

Brant is telling us how the night before Kurt killed himself he came to him in a dream: "Kurt said it was time to pass the torch on to me." Brant strums the guitar and then contorts his face in pain. He's singing (I think): "Pace in faith, I shared ..." No one has a clue what he's saying.

Down the road lives Katya, a grunge scene groupie, surrounded by large, quite disturbing paintings of cats. Katya went one better than Brant and claims to have met Kurt the day before he died. "He seemed very up, very positive", she says. Really?

Didn't that strike you as a little odd, given that he was just 24 hours away from committing suicide? "No, what struck me most was his luminosity." Luminosity? "Yeah, and the sparks." That's right. Sparks. According to Katya, Kurt had sparks coming off his head.

Brant and Katya are just two of the otherwise sane, ordinary people who claim to have either seen or shared some spiritual communion with Kurt Cobain in the last days of his life.

These last days have become a key component in the deification of Cobain. Nobody knows what actually happened to him between April 1st, when he jumped the wall of rehab, and the 8th (when his body was discovered), so the last days serve as a kind of rock equivalent of the stations of the cross, each movement or sighting loaded with almost religious significance.

Kurt's sanctification has gone into overdrive - a dozen films, books, even an Action Man-style doll dressed like Kurt in the Teen Spirit video. Plus, of course, the ever-growing ranks of disciples: thousands of teenagers wearing Kurt and Nirvana hoodies. There are tons of trinkets, but nothing definitive about what happened to him in the last days.

I first got interested in this stuff while making another film in Seattle. The more I heard rumours about Cobain's last seven days, the more it sounded like a kind of warped Keystone Cops caper.

There were stories: about Cobain dodging private investigators hired by Courtney, Kurt hiding shotgun shells with cab drivers, and bizarre sightings of Kurt pointing at eagles in the sky. Even of him licking plates in restaurants. I was convinced there was a film in all this and approached the editor of a now defunct BBC arts strand, who said, in effect: "Who'd want to watch that?"

In desperation (and total naivety) I met Nick Broomfield in a pub, who thought it a great idea, and then promptly went on to make a film focusing on the conspiracy theories. An indecent amount of time later, and after just about everyone in Seattle has either moved on, died of a drugs overdose or cut their hair and become a mortgage advisor, I finally got to make the film. It goes out on BBC2 in December.

Feature doc director John Dower, who made the Britpop film Live Forever (and, more recently, Once In A Lifetime, about the phenomenon of the New York Cosmos soccer team), foolishly agreed to direct it. And so off we went, without a single interviewee. Courtney Love declined, quite sweetly. "I don't want to do the rock widow thang anymore," she said. Unlike Broomfield, at least we weren't going to get into a fight with her (which was lucky, because I'd definitely come off worse).

In Seattle, we met up with Duff McKagen, bassist in Guns N' Roses who'd bought a ticket on Delta Flight 788 to Seattle on April 1st 1994, and found himself sitting next to a crumpled figure wearing sunglasses.

It was the first irony of Cobain's final week. Having jumped the wall of the Exodus Recovery Center near LA (a kind of Priory for big American rock stars), Kurt found himself sitting next to a junkie rock star on the flight home. Duff is amazingly frank about what happens when two drug addict musicians meet up on a plane. "You cop some dope and then talk about quitting ... 'Yeah, this is the last time right?'"

Like Duff, Kurt was forced into rehab by an intervention. Following a failed suicide attempt in Rome, Cobain was confronted by wife Courtney and the band with a chilling ultimatum: give up heroin, or you will never see your daughter, Frances Bean, again.

It took this prospect to force Kurt into Exodus, but he only lasted a day, jumping over the wall (he could have walked out - the doors were open. He chose to jump over the wall). We spoke to his counsellor Nial (it's the first time he's ever spoken on camera). Nial said that Cobain was nowhere near facing up to his addiction. Duff agrees: "Addiction? It wasn't an addiction, right?"

Back in Seattle, Cobain proceeded to start scoring inordinate amounts of heroin, heading on out to the seedy-as-fuck Aurora Avenue to score them in Room 226 of the Marco Polo Motel (checking in as "Bill Bailey", the real name of Axl Rose).

Apocryphal stories abound that Kurt hired a succession of cabs to ferry him round town on a kind of Death in Venice-like long goodbye (this is untrue). More fancifully, he'd been seen with hookers (also untrue) and even gained final absolution from a priest (yup, that's a load of bollocks too). The truth is Kurt holed himself up with the bags of scag in 226: his only bolt-hole from the madness of his life, where he prepares for his death.

The day before he commits suicide, Kurt makes a bizarre foray to the Cactus Restaurant. We interviewed a nice lady called Ginny who saw Kurt licking his plate. The owner, Bret, says Kurt had pudding first (the classic junkie order). When he came to pay (he was off to see a movie - The Piano) his card was declined (Courtney had it cancelled). Kurt seemed to fall asleep midway through writing the cheque.

Kurt seemed prepared for the following day. This is backed up by Victoria, who made the last authenticated sighting of Kurt alive, outside Linda's Bar on Capitol Hill, later that evening. "I said 'Hi, Kurt. Come for my party?' and he just went 'No' and walked to the back of the bar. People say he went on the roof to 'contemplate life' but he didn't. He just seemed utterly normal."

None of these people have appeared in any films before, largely because no one had ever bothered to ask them. This is because the Kurt industry has been obsessed with the rock cliches of The Man Behind The Myth rather than the tiny details of the last days that add up to a different portrait. For conspiracy theorists, it's simply unfeasible that Cobain committed suicide (more likely it was Courtney who had him murdered, possibly with Princess Di pulling the strings).

But guess what? He did. Kurt was just a man who killed himself, but he was also a lot of other things. He was a drug addict since day one (he was prescribed Ritalin as a child). He was a born again Christian, was into 1960s pop crooner Bobby Sherman, and briefly ran a hugely unsuccessful cleaning business. He was also far from the little boy lost loser he professed to be: though he publicly dissed MTV, he spent hours phoning to complain they didn't play his videos enough. All true, but none of it fits the myth of a holy junkie.

Kurt loved small animals and hated his biggest hit, Smells Like Teen Spirit (he nicked the chords off Boston's More Than A Feeling). And when he killed himself, he became bigger than anyone (in 2006 he outgrossed Elvis for the first time). He would have turned 40 this year. It would have amused him to know you can now buy an Action Man of him with torn jeans and lanky hair, aged 27 forever. He would have had a good laugh about it (plus made sure he got a good deal on the payments). That was the Cobain we found, and maybe it was something approaching the real thing.

Sighting talk: Those who 'connected' with Kurt in his final days

Katya

Grunge scene groupie who links herself not just to Kurt but a whole host of Seattle luminaries. Is privy to loads of their secrets through dreams. Just won't tell us exactly what.

Tom Grant

PI who failed to spot that Kurt was in his greenhouse, dead. Has now made a tidy sum leading the conspiracy industry, ie, Courtney dun it (she didn't, Kurt Dun It).

Sandy and Kathleen

Tie-dyed 60-somethings who make the Grateful Dead look sprightly. They're keeping the candle alive for Kurt, quite literally.

Brant

Fan who showered on many of the same days as Kurt. The similarities, well, end there.

Jake

Housewife who's made it her life's work to know everything about Kurt and Courtney.

Duff McKagen

Guns N' Roses bassist who found himself sitting next to Kurt on a plane. Duff's spleen had exploded as a result of substance abuse, so they had plenty to talk about on the flight.

· The Last 48 Hours Of Kurt Cobain will be shown on BBC2 in December