The footage shows a man believed to be Dorner dumping items in a garbage bin, including an ammo magazine and a military belt.
The video was taken Monday outside an auto parts shop in National City, south of San Diego one day after the murders of a young couple in Irvine.
Store owner Majid Yahyai said one of his employees found the items when he went to throw away the trash.
"He came back with a clip, like a magazine, full of bullets, a belt, a military belt and a helmet," Yahyai described.
Those items and that surveillance tape have been turned over to police.
Monica Quan and her fiancé, Keith Lawrence, were found shot to death Feb 3 inside a car in the parking garage of their apartment complex in Irvine.
Dorner, an ex-LAPD officer, is the prime suspect in the killings. Quan is the daughter of an LAPD captain who represented Dorner during disciplinary hearings, which resulted in his dismissal from the department.
Authorities say Dorner wrote a multi-page manifesto in which he threatened to kill law enforcement officials and implicated himself in the Irvine slayings. He accused of shooting three police officers last Thursday, killing one.
Authorities emphasize that Dorner is armed and considered extremely dangerous. If seen, do not attempt to contact him and call 911.
Anyone with tips on Dorner is asked to contact the LAPD at (213) 486-6860 or email firstname.lastname@example.org.