LOS ANGELES  To her neighbors, she was the kindly friend who delivered chocolate-covered cherries at Christmastime and passed hours in the garage building doors and cabinets. To her colleagues, she was a basketball-crazed jokester who threw herself into work but delighted in pranks like kidnapping a stuffed bear for a candy “ransom.”

But to the police and prosecutors, Stephanie Lazarus, the 49-year-old mother of a toddler whom friends and co-workers could not praise enough, is a killer. Worse, she is one of their own. She is a Los Angeles police detective, and she has been charged with killing the wife of a former lover more than 20 years ago.

Deputy Chief Charlie Beck, who supervises hundreds of detectives and has seen his share of sensational crimes in a 32-year career here, is still shaking his head at the whirlwind turn of the case.

Only a few police officers in Chief Beck’s career have been charged with deliberately killing someone off duty, and he never imagined investigating one of his own seasoned detectives for such a crime.