Officer Daniel Ackerman, 31, was participating in a SWAT physical training exercise at about 8 a.m. Friday when he showed signs of exertion and was rushed to St. Jude Medical Center in Fullerton in critical condition.
Authorities said Ackerman, a Tustin resident, died at 3:40 a.m. Saturday.
Ackerman joined the Buena Park Police Department as a police explorer in October 1995. He became a reserve police officer in April 2001 and was hired as a full-time police officer in June 2005. He is survived by his mother, sister, daughter and extended family.
Authorities said the Orange County Coroner will investigate the cause of Ackerman's death.