Richard Anthony Sepolio -- a 24-year-old on-duty Navy serviceman stationed in Coronado -- was arrested on suspicion of driving under the influence, causing injury or death. He could face four counts of vehicular homicide, according to the California Highway Patrol.
On Saturday afternoon, Sepolio's truck plunged off the Coronado Bridge and landed in the park, where hundreds of people were attending the La Raza biker festival, authorities said.
Alcohol was involved, CHP spokesman Jake Sanchez said during a Saturday press conference.
"It's horrible," Sanchez said. "Innocent people were down here having a good time -- now, they're gone."
Authorities identified the four deceased as Cruz Elias Contreras, 52, and Annamarie Contreras, 50, both from Chandler, Arizona and Andre Christopher Banks, 49, and Francine Denise Jimenez, 46, both from Hacienda Heights.
Investigators used a curtain to surround an area where the truck landed.
The GMC truck landed on its side on top of four people, according to Chief Brian Fennessy of San Diego Fire-Rescue.
People attending the festival were able to get the badly damaged truck upright, Capt. Chuck Kaye of the San Diego Police Department said.
Police officers gave medical aid to those crushed by the truck, "but to no avail," Kaye said.
Sepolio suffered major trauma and is being treated for his injuries at UC San Diego Medical Center, Sanchez said.
The injured victims were taken to either UC San Diego or Scripps Mercy hospitals for treatment, said Lee Swanson, spokesperson for San Diego Fire- Rescue Department. All the injured victims are adults, authorities said. Their conditions also were unavailable.
The crash was reported shortly after 3:30 p.m.
Sepolio -- said to have been alone in the pickup that has Texas license plates -- was going southbound on Interstate 5, heading for the Coronado Bridge when he failed to make the transition and crashed, Swanson said.
The crash caused so much chaos that both the Coronado and Harbor police departments were called in to help.
A CHP officer told reporters that no police officers were pursuing Sepolio before he crashed.
San Diego Mayor Kevin Faulconer sent out a tweet Saturday, saying "praying for victims & families affected by tragedy in Chicano Park. Devastated this occurred in one of our community's most beloved places."
**WARNING: Video contains graphic language**