Deputies responded to the shooting, and when they arrived at the scene, they discovered O'Connell suffering from a gunshot wound to the chest.
He was pronounced dead at the scene.
WIFE OF CALIFORNIA DOCTOR WHO DROVE FAMILY OFF CLIFF IN TESLA DOESN'T WANT HIM PROSECUTED: REPORTS
Bishop David O'Connell was shot do death on Sunday. (Sarah Reingewirtz/MediaNews Group/Pasadena Star-News via Getty Images)
"It's very early in the investigation," sheriff's department Homicide Bureau Detective Michael Modica said Sunday. "We got a lot more steps we have to take to make more determination to what's happening."
CA CONVICTED KILLER DIAGNOSED WITH TERMINAL CANCER TO BE RELEASED
O'Connell, 69, was named Auxiliary Bishop of the Archdiocese of Los Angeles by Pope Francis in 2015.
This is a developing story. Check back soon for updates.