Craig Voss, 71, of San Diego, also faces five counts of causing great bodily injury while committing a felony and one count of driving under the influence, Nisleit said.
Three people died at scene in downtown San Diego and six others were injured, Fire Chief Colin Stowell said.
Mayor Todd Gloria said most or all of the people gathered on the underpass sidewalk were homeless.
Nisleit said many of the people were seeking shelter from the rain in the tunnel.
“I don’t know if people were sleeping, if people were sitting there,” Nisleit said. He said it appeared several tents and personal belongings were placed along the sidewalk.
After the vehicle ran into the crowd and came to a stop in the road, the driver of the Volvo station wagon attempted to render aid and identified himself to officers, the police chief said.
The driver was cooperative and didn’t try to leave the area, the chief said at an earlier news conference. Authorities said initially that the driver had fled the scene before being detained.
The police chief said at least two people who were taken to the hospital were in critical condition.
Police received a radio call several minutes before the crash, about a vehicle matching the description of the Volvo, but officers were not following him at the time of the incident, Nisleit said.
He said the car “for whatever reason, it veered to the right and went completely up onto the sidewalk.” The car went back into the road where it stopped and the driver got out, Nisleit said.
The incident, reported just after 9 a.m. PT, happened in the 1500 block of B Street near San Diego City College.
“I’m like whoa! Is this guy ever gonna stop?” Williams said the driver exited his car and hid his face and “casually walked away.”
Another witness, Michael Luke, told KGTV the driver stayed at the scene and looked distraught.
“I saw the wagon move over and things just started popping up .. and the dragging … Horrific,” said Luke.
The investigation is ongoing.