The film is being released to coincide with the 30th anniversary of the death of Sid Vicious. Trailer courtesy of Ipso Facto Films
By Liam Allen
Entertainment reporter, BBC News
On the 30th anniversary of the death of Sid Vicious, director Alan G Parker says his new film Who Killed Nancy? strengthens the claim that the Sex Pistols bassist did not kill Nancy Spungen.
On 2 February 1979, 21-year-old Vicious was found dead in an apartment in Greenwich Village, New York, by his mother Anne Beverley.
To be honest with you, I think this film had to be made from about the day that Sid's mother died in 1996
He had overdosed on heroin after a party to celebrate his release on bail, a day earlier. The punk rocker was facing trial for the murder of girlfriend Spungen in October of the previous year.
After his death, the police closed the case.
Parker says that since then, the public has assumed that Vicious - born John Ritchie - killed Spungen.
In 1985, while he was working as a punk rock journalist, Parker was asked by Vicious's mother to prove her son's innocence.
"To be honest with you, I think this film had to be made from about the day that Sid's mother died in 1996," the 43-year-old says.
From then on, he says he treated the request from Anne Beverley as if it were "her last wish".
The body of Spungen, 20, was found on 12 October 1978 in a room at New York's Chelsea Hotel where she and Vicious had been staying. Dressed in just her underwear, she died from stab wounds to her stomach.
Hotel staff said Vicious had called room service to raise the alarm and had then run downstairs saying: "Something's happened to my girl."
Spungen and Vicious had been living in room 100 at the Chelsea for six weeks
He was arrested and charged with murder on the same day.
Parker, who has written two books about the Sex Pistols bassist, says he did not believe Vicious was innocent until about 1999, when he started gathering more accounts.
He says the scores of people he spoke to for his documentary - including some who say they were at the Chelsea Hotel and others who claim they were at Vicious's party on the night he died - have strengthened his belief.
"Realistically, the worst title in the world for this film is Who Killed Nancy? What it should have been called is who didn't kill Nancy and here's 500 reasons why," he says.
Parker says the film has thrown up a number of theories which support the notion of Vicious's innocence.
He may have taken 30 painkillers and was "out cold" for more than seven hours - including the timeframe when Spungen was killed, while $24,000 in cash went missing the night she died.
It is also claimed that only four of his fingerprints were found by police in their hotel room, despite the fact the couple had been living there for weeks.
Sid Vicious (second left) replaced Glen Matlock as bassist in the Sex Pistols
So who did kill Nancy Spungen?
Parker says accounts uncovered in his film suggest the killer was someone called Michael - "we don't know his second name, we just know he was around".
"He was flashing a lot of money, he was bragging about having robbed the room and Sid was there and Nancy was dead and everything.
"People saw him on the night as well - we've got witness statements.
"He was seen in the room, outside the room, on another floor in the Chelsea, bragging about getting all this money together, which he showed to someone wrapped up in Nancy's hair tie."
The original motivation for the film - Anne Beverley's plea to Parker to clear her son's name - will inevitably lead to claims of bias.
"To be honest with you, I can understand anyone thinking it but I don't want to go down that road for the simple reason that there's no real point in making it if I'm that biased."
He admits he is "a big Pistols fan".
"But not big enough a fan to want to change history."
Who Killed Nancy will be out in cinemas across London on Friday 6 February. The book it is based on, Sid Vicious: No One Is Innocent, is out now.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.