SANTA MONICA, California (CNN) -- An 86-year-old man who drove his mid-size Buick through a crowded farmers market Wednesday told police he couldn't stop and may have hit the accelerator instead of the brake, Santa Monica Police Chief James T. Butts Jr. said.
Nine people were killed, including a 3-year-old girl, authorities said. The more than 54 hurt include 14 people with critical injuries, they said. Two of those critically injured are under the age of 2.
"He said that he tried to brake and he couldn't stop the vehicle," Butts said.
Police escorted the man, identified by his attorney as Russell Weller, to a local hospital where he was found to have no alcohol or psychiatric medications in his system.
Later, Weller walked out of the police station with the help of a cane and with his attorney by his side. Police released him from custody after he was interviewed by detectives. Charges could be filed at a later time, Butts said, noting that Weller is a resident of Santa Monica and does not appear to be a flight risk.
"Right now it looks as though there may be some negligence as far as his capacity to drive safely," Butts said. There was no indication that Weller intended to injure any pedestrians.
The driver's attorney, Jim Bianco, released a statement from the family late Wednesday:
"Mr. Weller and his family want to express their deepest sympathies to the victims and their families of the tragic accident earlier today. This was an unintentional and unfortunate accident. Mr. Weller is very shaken up, but his thoughts are with the victims and their families."
He declined any further statements, in light of the ongoing investigation, with which Bianco said "we are cooperating fully."
Butts said Weller drove his 1992 Buick LeSabre "at least at a moderate rate of speed" for three blocks along the market street, which was filled with pedestrians, "striking dozens of people." The car stopped only after a pedestrian was thrown into the air and landed on the windshield of the vehicle, Butts said.
The accident occurred at 1:47 p.m. (4:47 p.m. EDT), Butts said.
Butts said officers have interviewed more than 100 witnesses, who gave conflicting reports regarding the driver's demeanor at the time of the incident.
"So now we're attempting to determine whether this was a straight accident -- medically related -- criminal negligence or criminal homicide," Butts said.
One witness said: "It was like a Sherman tank barreling through, hitting everything, just going right over people.
"He was not only speeding, he was accelerating."
Joe Chrisman works in a building along the street where the market is held. He witnessed the accident and said the driver appeared befuddled.
"He looked very, very confused," Chrisman said. "I think he was just mentally out of touch. He seemed very confused when he stepped out of the car. He definitely shouldn't have been behind the wheel. He was definitely not quite with it."
Chrisman said there was a woman underneath the man's car, and after a bicycle policeman apprehended the driver, a group of about 10 people together lifted the car off of the victim, who was still breathing.
Video shot by local news station helicopters showed several people being treated by emergency personnel on top of red sheets in the street. Ambulances and police cars crowded the area, and a damaged red car sat among debris.
As police roped off the crime scene, a child's blue stroller sat empty in the street amid bodies covered with yellow tarps.
"This is the single most horrific, devastating scene of tragedy I've ever witnessed in 30 years of law enforcement," Butts said. He added that the sight of the dead child "just broke my heart."
Chrisman said he ran outside to help after the accident.
There was "so much carnage," he said.
Nine of the injured were taken to St. John's Health Center, where one of them -- a 50-year-old man -- died Wednesday night, according to Lt. Ed Winter of the the L.A. Coroner's Office.
UCLA Medical Center received 13 patients: Six in critical condition -- including two children under the age of 2; two patients who were still being evaluated; and five people who have been treated and released.
UCLA Santa Monica received 12 victims: one infant in critical condition; four adults in serious condition; and seven people with minor injuries.
Hospital sources said the injuries range from broken bones to head injuries to possible internal injuries.
A spokeswoman for the Santa Monica Police Department said the Wednesday market is usually extremely busy, with three city blocks devoted to the market stalls and closed to all but pedestrian traffic.