Lt. Kenneth Alexander, 48, had been at St. Jude Hospital's Critical Care Unit since Tuesday and was on life support, Placentia police said. The department announced his death shortly before 9 p.m. Sunday on Twitter.
Alexander was a decorated Army veteran who served two tours in Iraq and one tour in Afghanistan. He was a Bronze Star recipient, and he also received the Medal of Valor in 1996 while working with the Los Angeles Housing Authority Police.
Alexander was also a longtime DARE and North County SWAT officer.
He is survived by his wife, three sons, mother, two brothers and sister.
Officers transported Alexander's body at 12 p.m. to McAulay & Wallace Mortuary in Fullerton. His funeral services are pending.