The truck rolled backwards down a steep section of Divisadero Street between Vallejo and Broadway last Tuesday.
Police say the truck smashed into nine parked cars before crashing into a tree on a sidewalk. Three people suffered minor injuries in the incident.
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The investigation found the truck was overloaded and the emergency brakes malfunctioned.
Additionally, investigators say the driver ignored safety precautions by not curbing the tires or chocking the wheels.
An SFPD source says the company has had "prior safety violations."