The announcement by Beverly Hills police marks a major break in an investigation that has baffled detectives for nearly a month and stunned Hollywood ever since Ronni Chasen was gunned down while driving home from a movie premiere in her Mercedes in November.

Sgt. Mike Publicker said it was a “robbery gone bad” committed by Harold Martin Smith, who has a rap sheet dating back at least 25 years. Police Chief David Snowden also said the gun used by Smith to commit suicide appears to have been used to kill Chasen.

“We believe that Mr. Smith acted alone. We don’t believe it was a professional hit,” he said.

Chasen was shot multiple times in the chest Nov. 20 as she drove through Beverly Hills after returning home from a premiere of the movie “Burlesque.”

Publicker said investigators believe Smith, riding a bicycle, tried to rob Chasen as she waited to turn left off of Sunset Boulevard.

“This was a random act of violence, with Mr. Smith’s background, we believe that it was most likely a robbery gone bad at this time,” he said.

“Through the interviews and the information we received, that leads us to believe that he was at a desperate point in his life, and was reaching out and doing desperate measures,” Publicker said.

Chasen, 64, was an influential behind-the-scenes player in Hollywood with her long track record in promoting films and their stars for the Oscars. The movies included “Driving Miss Daisy,” the sequel to “Wall Street” and “On Golden Pond.”

Police said the information leading detectives to Smith was an anonymous tip to “America’s Most Wanted” and that person may be eligible for a $125,000 reward.

Police confirmed that no shell casings were found at the scene. They did not reveal whether there was any video evidence.

Smith, 43, had been described by police as a “person of interest” after bragging to acquaintances that he killed Chasen. Documents obtained by The Associated Press revealed Smith was a two-strike felon with a criminal history that dates back at least 25 years.

He had been convicted twice of burglary and most recently had been released from prison in 2007 after serving time for robbery.

Police stressed that their investigation is ongoing.