TUSTIN, California - A 20-year-old student wielding a shotgun shot and killed a woman in her home and two commuters during carjackings, shot up vehicles on a Southern California freeway and committed suicide as police closed in on him Tuesday, authorities said.

The early-morning killings happened not long after a bloody saga that gripped Southern California for six days, as former Los Angeles police officer Christopher Dorner eluded a massive manhunt after killing three people. Dorner died February 12 from an apparent self-inflicted gunshot wound to the head after a fiery gun battle that left one police officer dead.

Police authorities process a black car, next to a stolen white car (R), in the parking lot of a Tustin computer store after a gunman went on a shooting spree in suburban southern California Feb 19, 2013. [Photo/Agencies]

On Tuesday, a driver was forced from his BMW at a stop sign, marched to a curb and killed as witnesses watched in horror.

"He was basically executed," Santa Ana police Cpl. Anthony Bertagna said. "There were at least six witnesses."

The shooter, Ali Syed, was an unemployed, part-time student who lived with his parents at the Ladera Ranch residence where the first victim was slain, Tustin police Chief Scott Jordan said. Authorities said Syed was taking one course at Saddleback College, a two-year community college.

Orange County sheriff's spokesman Jim Amormino said the woman killed at the home was in her 20s. She was not identified and was not related to the shooter, he said, adding that it wasn't known what she was doing at the home.

Syed's parents were in the house at the time, fled the residence when shots were fired, and reported it, he said.

Jordan said Syed stated to one carjacking victim: "I don't want to hurt you. I killed somebody. Today is my last day."

Jordan said there was no indication of a motive, but he sought to assure residents that the violence was over.

The shooting spree apparently didn't involve an assault weapon like those used in a series of recent mass killings. But it comes as Americans have been embroiled in a fierce debate over gun violence, as the Obama administration wages an uphill battle to get Congress to approve new gun control laws.

On Tuesday, Vice President Joe Biden responded to a question from a Facebook user during a forum by saying the administration's proposal to ban military-style assault weapons and high-capacity magazines would not make law-abiding citizens a more vulnerable target of criminals. Biden said he keeps two shotguns and shells locked up at home and encouraged those worried about defending themselves to buy a shotgun.

The latest highly-publicized shooting began at 4:45 am local time, when deputies responded to a call from Ladera Ranch, a sleepy inland town southeast of Los Angeles. They found the woman shot multiple times.

The gunman then headed north and within 30 minutes carjacked a Dodge pickup truck in Tustin, about 20 miles (32 kilometers) away, police said. The driver was uninjured, but a bystander was hit by gunfire and taken to a hospital.

The suspect then began firing at vehicles in the area where Interstate 5 and State Route 55 connect.

Three people reported being targeted, including one who suffered a minor injury, Tustin police Lt. Paul Garaven said. Two cars were damaged.

When the gunman's truck got low on gas, he stopped in Santa Ana, stole the BMW and killed the driver, Bertagna said.

The victim was identified as Melvin Edwards, 69, of Laguna Hills, who was en route to his Santa Ana business.

The shooter then drove to a Tustin business called Micro Center and stole another small truck, killing construction worker Jeremy Lewis, 26, of Fullerton, and wounding another person.

Officers trailed the gunman to Orange, a city about five miles (8 kilometers) away.

As they closed in, the man got out of the vehicle at a busy intersection and shot himself, police said.

A shotgun was recovered at the scene.