The actress killed at music producer Phil Spector's US home in 2003 was shot with a gun inside her mouth, according to the coroner's report.
Spector (right) is pictured with one his lawyers, Leslie Abramson
Lana Clarkson also had gunshot residue on her hands, said the report prepared four days after her death.
Mr Spector's defence lawyers are likely to suggest Ms Clarkson shot herself, although her blood and gunshot residue were also found on Mr Spector.
Mr Spector was charged with murder in November and is on $1m (£550,000) bail.
The autopsy details were sealed at the request of prosecutors, but Spector's lawyers Leslie Abramson and Marcia Morrissey released the report to the media.
"There is certainly no justice in maintaining this
secrecy in the light of Mr Spector's being charged with
murder," they said.
The report stated that "the deceased may have discharged a firearm or had (her) hands otherwise in an environment of gunshot residue".
Lana Clarkson died in February 2003
It also showed that analysis of blood found on the gun's exterior and inside the barrel matched Ms Clarkson's DNA.
But the report still concluded that "the manner of death is homicide".
It said law enforcement reports indicated that Ms Clarkson's "male companion" had possession of the gun when it was discharged.
Sandi Gibbons, spokeswoman for the Los Angeles County District Attorney's Office, said prosecutors did not dispute that the gun was in Ms Clarkson's
"It does not mean she put it there," Gibbons said.
"We're fully aware of the contents of the autopsy report
and we intend to proceed with this case," she added.
Ms Gibbons also said that a gunshot releases a cloud of residue within a three-foot radius.
Other reports in the coroner's file showed that
Clarkson had alcohol and the prescription painkiller
Vicodin in her system when she died.
Mr Spector protested his innocence and suggested Ms Clarkson killed herself in an interview with Esquire magazine last year.
He pleaded not guilty to the B-movie actress's murder during a brief hearing in Alhambra, near Los Angeles, in November.
Mr Spector made his name in the 1960s when his Wall of Sound technique transformed pop music.
He was responsible for producing acts such as the Beatles and the Ronettes.