The 64-year-old was shot dead in her car about 12:30 a.m. Tuesday in Beverly Hills. She was on her way home from a party after attending the premiere of the new film, "Burlesque."
Beverly Hills Mayor Jimmy Delshad said detectives believe the bullets came from an SUV because of the high angle of shots fired.
Police found some pieces of glass near the shooting site, but found no bullet casings, Delshad said.
Delshad said detectives had a theory that Chasen was turning left from Sunset Boulevard onto Whittier when a gunman from another car shot from the passenger window and hit her five times in the chest.
"It looks like it happened from the right passenger window," Delshad said.
Many jurisdictions in the area have offered the Beverly Hills Police Department their help, including the Los Angeles County Sheriff's Department and Office of the District Attorney, but Beverly Hills police have turned them down.
The Palm Springs International Film Festival on Wednesday offered a $100,000 reward for information leading to the conviction of her killer.
Publicist Michael Levine on Tuesday started a fund and hoped to raise $25,000 by the end of the week.
Meantime, Delshad said people should feel safe in Beverly Hills.
"People should feel very comfortable about coming to Beverly Hills and should not worry about their safety," Delshad said.
Anyone with information related to the incident is urged to call the Beverly Hills Detectives Hotline at (310) 288-2656.
The Associated Press contributed to this report.