An unidentified witness captured the chaotic moments after a horrific crash in San Diego when a truck plummeted off a freeway bridge Saturday, killing four people at a festival.

Among the dead are Cruz Elias Contreras and Annamarie Contreras of Chandler, Arizona.

SEE: 2 Chandler residents killed in 'horrific' San Diego crash

Also killed were Andre Christopher Banks and Francine Denise Jimenez of suburban Los Angeles.

The pickup driver, Richard Anthony Sepolio, was arrested on suspicion of driving under the influence causing death.

The tragedy occurred at a biker festival called La Raza Run, an annual motorcycle ride from Los Angeles to San Diego that can draw more than 1,000 bikers.

The video, originally posted to Facebook and obtained by NBC News, shows people scrambling to pull Sepolio from the wreck amid a chaotic initial response by witnesses and police.