PIEDMONT, Calif. (AP) -- Drug use and excessive speed were to blame for last year's fiery crash of a Tesla Cybertruck that killed three college students near San Francisco, the California Highway Patrol said in a preliminary report.

Four people were in the Cybertruck when it veered off a road, slammed into a retaining wall and burst into flames shortly after 3 a.m. on Nov. 27 in Piedmont.

"Officers determined that a combination of driving under the influence of drugs and unsafe speed were the causes" of the crash, the highway patrol said in a statement last week.

Although police officers who responded were unable to douse the flames with their fire extinguishers, the fire department put the blaze out quickly, officials said at the time.

Piedmont Fire Chief Dave Brannigan said the day after the crash that the speed in extinguishing the flames meant it was unlikely that the Cybertruck's large lithium-ion battery had caught fire. He called the incident "more along the lines of a typical car fire."

Killed in the single-vehicle crash were Soren Dixon, 19, Jack Nelson, 20, and Krysta Tsukahara, 19. The fourth occupant, Jordan Miller, 20, survived after someone in another car managed to pull him out of the wreckage. All four were home from college for Thanksgiving break and graduates of Piedmont High School, the San Francisco Chronicle reported Sunday.

The Chronicle cited toxicology reports that determined the three victims who died had alcohol, cocaine and other substances in their system. Their deaths were ruled an accident because they were caused by asphyxia due to inhalation of smoke from the car, and burns were a "significant" factor in their deaths, the autopsy report said.

The highway patrol's investigation is ongoing and a final reported is expected within months, the agency said.

The Cybertruck, which has been available for purchase for more than a year, has been recalled multiple times for safety problems, including once in November because a fault in an electric inverter can cause the drive wheels to lose power. Last April, the futuristic-looking trucks were recalled to fix gas pedals that can get stuck in the interior trim.