Prosecutors allege that the 31-year-old CHP officer shot Lemons on a 91 Freeway off-ramp and then drove to her parents' house in Compton.
Deputies discovered Lemons' body in the front passenger seat. He had been shot in the head.
Authorities say Johnson was off duty at the time of the shooting and intentionally discharged a handgun, killing her husband on Feb. 21, 2009.
Johnson told investigators her husband was verbally and physically abusive, and friends say she was just protecting herself.
Johnson worked out of the West L.A. office. Since the shooting, she had been in a non-enforcement administrative position. Tuesday, she was placed on administration leave without pay. She remained behind bars on $2 million bail.