AUGUSTA — Police on Monday interviewed customers and other people who might have clues to why an oil delivery truck ran off a 75-foot embankment and crashed in a ravine, killing the 22-year-old driver, but the cause remained a mystery.

An autopsy showed that the driver, Robert T. Davis of Augusta, died of multiple injuries.

The Gagne Fuel Oil Corp. truck apparently traveled through a densely populated residential neighborhood before going over the embankment at the end of a dead-end street Friday afternoon, although the wreckage was not discovered until a Maine Warden Service pilot spotted it Saturday.

“Nobody saw it happen, obviously,” said Augusta police Lt. Gregory Locsin. “We only have one statement from a neighbor who said she saw the vehicle in the neighborhood around 3:30 p.m., according to her, and then she went back to doing her housework.”

More than 1,400 gallons of home heating oil were pumped out of the truck before it was lifted out of the ravine by a crane on Sunday morning, police said.

Augusta police said investigators were interviewing neighborhood residents and customers to whom Davis had delivered oil Friday in hope of determining the cause of the crash. Capt. Francis Malinowski said police also were seeking a search warrant in order to examine the mechanical condition of the truck.