Chasen, 64, was fatally shot Nov. 16, 2010, as she drove her Mercedes-Benz coupe through Beverly Hills on her way home from a film premiere.
The autopsy report released Thursday by the Los Angeles County coroner's office said that homicide detectives initially suspected Chasen was waiting for a red light when someone drove up next to her and fired four gunshots through her passenger window.
The Los Angeles Times says the report was released as part of a settlement with a documentary filmmaker who sued to see it.
With no witnesses and almost no leads, investigators interviewed her friends, family and professional contacts and searched her home and workplace to find a motive. A tip to the show "America's Most Wanted" ultimately led investigators to an ex-con who shot himself in the head when they tried to question him on Dec. 1, 2010.
Ballistic tests revealed the gun Harold Martin Smith used to shoot himself was the same weapon used to shoot Chasen in the chest.
Police concluded that Smith killed Chasen as part of a robbery attempt, but did not take anything and fled on a bicycle before anyone could see him in the early morning darkness.