Jack Romero, 33, of Santa Rosa, worked as a corrections officer in Sonoma County Jail from 2002 to 2008, when he resigned amid an internal investigation, Assistant Sheriff Lorenzo Duenas said.
Duenas said he could not disclose the nature of the probe.
"He was involved in an internal investigation that could have resulted in disciplinary action up to and including termination, and he resigned in 2008," Duenas said.
Romero was involved in a brief argument just outside Third Street Aleworks at 610 Third St. late Tuesday, Sgt. Steve Fraga said.
He was chased and shot multiple times as he ran from the pub, Fraga said. His body was found just after midnight Wednesday in a breezeway near a parking garage at the northwest corner of Second and D streets, Fraga said.
Through witnesses, police identified 29-year-old Ryan Mitchell Dietz, of Santa Rosa, as a suspect, Fraga said.
Dietz was located at his place of employment, Integrity Electric in San Rafael. He was arrested at 4:45 p.m. Wednesday at 2 Las Huertas Ct. where the residential and commercial electric installation company parks its trucks, Fraga said.
Police also arrested Dietz's girlfriend, Garicka Lavern Rush, 31, at her Amethyst Way home in Santa Rosa on suspicion of being an accessory to murder, Fraga said.
Dietz and Rush are scheduled to be arraigned Friday afternoon in Sonoma County Superior Court.
Dietz and Romero knew each other and were neighbors at one time, Fraga said. Dietz and Rush have three children and lived together.
"Romero and Rush have dated periodically over the past year, and Dietz has confronted Romero on this in a few verbal confrontations," Fraga said.
Police do not believe Rush witnessed the shooting or drove Dietz from the murder scene, Fraga said.
"He drove himself," Fraga said.
Romero's autopsy was scheduled for this morning.