25-percent of all that video collected was accidentally deleted during a system update two years ago, the Chronicle reported.
Police department officials say they are not aware of any cases that have been adversely impacted by the missing video.
The revelations came to light during police testimony in the murder trial of two men charged in the July 2013 killing of Judy Salamon several blocks away from her East Oakland home.
Officials do say videos that had been specifically marked as evidence or copied to external hard drives were retained.
Bay Area civil rights attorney John Burris, tells the paper the missing footage could pose a problem in some cases.