Arnold Cragmeyer (Christopher Boyer) is the head of the forensics lab and tends to always come through in helping Chase and August uncover clues and other useful information. He has a bachelor's degree is Forensic Science, and was previously a bomb squad commander in the premiere episode before requesting a transfer.
Det. Sam Richardson (Clay Banks) is another detective who assists Chase and August from time to time. He's originally from New York, but transferred to Los Angeles sometime prior to the third episode. Chase was the first cop he met and he wasn't too impressed with him, but he eventually grew to like him.
Det. Benny Lewis (Sugar Ray Leonard) was another detective who occasionally assisted Chase and August. He only appeared in the first, second, and fourth episodes before disappearing without explanation.
Annie Mason (Jessica Cushman) is a forensics assistant who joined midway through the first season. Her father is a detective in Riverside, California.
Dr. Judith Sands (Jessica Hopper) is the department's psychologist, whose assistance Chase and August sometimes require when dealing with the more crazed suspects. Her and Chase had a past relationship until he dumped her, claiming she was driving him crazy by always trying to get inside his head. She also had a somewhat successful (though short-lived) modeling career before becoming a psychologist.
Dr. Samantha Morecroft (Debbie James) is the new head coroner at the start of the second season. She's straightforward and to-the-letter, and is constantly put off by Chase's sly comments and flirting.
Det. Jack Lawson (Michael McFall) is a former D.E.A. agent who used his connection within the police department (his Aunt Grace, the police commissioner) to transfer to the department's robbery/homicide division. He thinks Chase is a little too on the reckless side, but ultimately comes to respect him.
Det. Nicole Stockman (Sandra Ferguson / Jillian McWhirter) is a beautiful but tough
San Francisco detective. She came to Los Angeles to deliver a witness to the LAPD. Initially finding herself in conflict with Chase and his methods, they eventually became friends over the phone and through weekend visits. At the end of the second season, she returned to Los Angeles to strike a deal with a crime boss in return for him testifying against Bobby Cole. Her and Chase were getting serious about her transferring to LA so she could move in with him, but she was killed in a hit ordered by Bobby Cole.
Bobby Cole (Gary Hudson) was introduced early in the second season and became the show's only recurring adversary. Known as the "Teflon crime lord," he was a notorious criminal with everyone from politicians to police officers on his payroll and could never be connected to any of his crimes. Everybody in the city knew he was a vicious criminal who had committed dozens of crimes, but no one could prove it. After numerous confrontations, his organization was finally broken down, and Cole was shot and killed by Chase in the series finale. ==Other appearances==