(CNN) -- In the middle of a shooting spree that killed three people and unleashed terror on Southern California motorists Tuesday morning, Ali Syed told one of his carjacking victims to walk away, police say.
"Mr. Syed ... said, 'I don't want to hurt you, I killed somebody. Today's my last day. Give me your keys,' " Tustin Police Chief Scott Jordan told reporters.
According to preliminary accounts from police, Syed, 20, didn't intentionally spare another target.
Police say they believe Syed, a part-time college student, fatally shot a woman at his family's Ladera Ranch home before killing two other people -- including a senior citizen executed outside his vehicle -- and wounding three others as he fired a shotgun at Orange County motorists on the Costa Mesa Freeway and committed three carjackings.
The spree ended when Syed died after he turned his gun on himself as police approached on a road north of Tustin, authorities say.
The Orange County Sheriff's Department says it was called to the Ladera Ranch home, where Syed lived with his parents, on a report of shots fired about 4:45 a.m. PT.
A woman in her 20s was found dead there. Police said she wasn't related to Syed, but they didn't release her name, and they said they didn't know why she was at the home.
Syed left the home in his parents' SUV, police said. About 25 minutes after that police call and 20 miles to the northwest, Syed drove into a Denny's and Big Lots parking lot in Tustin, exited the vehicle and shot a driver in the back of the head, Jordan said.
The wounded motorist -- a man who was waiting for his son to carpool with him to work -- managed to drive away before stopping near an overpass, Jordan said. The victim was being treated Tuesday, police said.
That's when Syed, whose SUV had a flat tire, approached the man he would spare. Syed ran toward the man at a nearby gas station, took his keys and drove the pickup truck away without firing at him, Jordan said.
Syed then drove south on the Costa Mesa Freeway, exited onto a transition road, got out of the vehicle and fired a shotgun at southbound vehicles on the freeway, hitting three vehicles, police said.
One of the freeway drivers was wounded in the hand and face, but investigators don't know whether the wounds were from shotgun rounds or debris, according to Jordan.
Police said Syed then drove to nearby Santa Ana, crashing the pickup into a curb on a freeway off-ramp. There, he pointed the shotgun at Melvin L. Edwards, 69, of Laguna Hills, who was in a BMW at a stop sign.
"Syed ... got (Edwards) out of the car at gunpoint, walked him across the road and executed him -- shot him three times," Jordan said.
Syed drove Edwards' BMW to the parking lot of a Tustin-area Micro Center computer store, where police said he found his next two shooting victims.
Syed shot and killed Jeremy Lewis, 26, of Fullerton, who was in a vehicle in the lot, police said. Lewis had worked at a construction site across the street.
People from the construction site then approached, and Syed shot and wounded one of them in the arm, Jordan said. Syed entered that person's vehicle and drove north on the Costa Mesa Freeway before exiting again.
By that time, authorities had received many phone calls about the shootings, and California Highway Patrol officers found Syed driving at an intersection about 5 miles north of Tustin, Jordan said.
Syed exited the vehicle as it slowly rolled near the intersection, according to police.
"There really wasn't a confrontation at that very end," Jordan said. "As soon as he got out of his vehicle, before it actually came to a complete stop, he shot and killed himself," Jordan said.
Syed was unemployed and taking one class at Saddleback College in Mission Viejo, an Orange County Sheriff's Department spokesman said.
Police said they're trying to determine what led to the shootings, and that they didn't yet know of a motive.
CNN's John Fricke contributed to this report.