In 75 minutes of terror, an Orange County gunman committed three murders and wounded three others before taking his own life Tuesday morning.

Police say 20-year-old Ali Syed, a college student, began his rampage in Ladera Ranch, where he murdered a young woman inside his parents' home.

Syed then drove to Tustin, Santa Ana and back to Tustin, carjacking three vehicles, killing two more victims and shooting indiscriminately at morning commuters on the 55 Freeway.

Then, with the California Highway Patrol in pursuit, Syed pulled off in Villa Park, aimed the shotgun at his own head, and pulled the trigger.

Authorities were stunned by what they described as the "senseless violence." Syed had no criminal record and left few clues as to a possible motive, police said.

Police discovered the first victim around 4:45 a.m. Tuesday at a condo on Red Leaf Lane in Ladera Ranch.

Syed, who was unemployed and enrolled in a class at Saddleback College, lived there with his parents. It was his parents who called 911, according to police.

"I heard three to five pops, and they could have been bangs, I didn't know what they were," said neighbor Scott Glass. "I didn't think anything of it."

That would change after responding Orange County sheriff's deputies found the body of a woman in her 20s who had been shot multiple times.

She was not related to Syed, authorities said, but it remains unclear who she was and why she was at his home.

Deputies were running her fingerprints through multiple systems to try to figure out her identity.

Meanwhile, Syed had taken off in the family's black GMC Yukon, armed with at least one shotgun, authorities said. Possibly in his haste to flee, police said, he damaged the vehicle.

He exited Interstate 5 at Red Hill Avenue in Tustin about 5 a.m. and pulled into a Denny's parking lot.

There, a man was sitting in an older-model blue Cadillac, waiting for his son to carpool to work.

According to police, Syed pointed his weapon at the man and ordered him out of the car.

Instead, the man sped away and Syed opened fire, shattering the rear window of the Cadillac and striking the man in the back of the head. The man was later treated at a hospital.

The gunman kept going to a nearby Mobil station, authorities said, where he spotted a man pumping gas.

"When they made eye contact, Syed started running toward the victim," said Tustin Police Chief Scott Jordan.

"He said to him, 'I don't want to hurt you. I just killed someone. Give me your keys. This is my last day,'" according to Jordan.

Syed took the man's Dodge pickup and headed north on Interstate 5, authorities said.

After merging onto the southbound 55 Freeway, he stopped on the shoulder, got out of the truck and opened fire on passing motorists.

He hit at least three cars, and one driver was injured by flying glass, according to police.

Santa Ana Police Cpl. Anthony Bertagna said the gunman may have realized that the pickup was low on fuel and was trying to steal a second vehicle.

He ultimately returned to the stolen pickup and got off the freeway at Edinger Avenue in Santa Ana.

He hit another vehicle, slammed into a divider and abandoned the truck, authorities said. Then he approached a BMW that was stopped nearby, with his gun drawn.

Melvin L. Edwards, 69, of Laguna Hills, was on his way to work at Rubicon Gear, a small family business that manufactures high-precision gears and shafts.

Colleagues described the former U.S. Army combat infantry officer who served in Vietnam as easygoing, hardworking and generous with his employees.

Syed ordered Edwards out of the BMW and directed him to the curb, authorities said. He cooperated, but the gunman killed Edwards anyways.

"Walked him across the road and executed him… Shot him three times," Jordan said.

The gunman then sped away in the BMW to a Micro Center computer store in Tustin.

Soon thereafter, workers at a nearby Fairfield Inn construction site heard gunfire.

A plumbing supervisor apparently spotted one of his co-workers being chased through an overflow parking lot and drove over to help him.

The co-worker, Jeremy Lewis, 26, of Fullerton, had just arrived for his 6 a.m. shift when, authorities said, Syed shot and killed him.

The supervisor who had gone to his aid was shot in the arm, police said. He was taken to the hospital to be treated for his wounds.

"It's just heart-wrenching to look across the street and see what I see now. It's bad. It's really bad," said a man who worked with the victims.

He said the victims were "just two good honest guys. They were just trying to make a living. Things happen so quick. One minute we're sitting on the tailgate, the next minute tragedy happens."

From there, Syed took off in one of the construction site's work trucks.

California Highway Patrol officers spotted him on the northbound 55 Freeway shortly before 6 a.m.

He exited the freeway at Katella Avenue and got out of the vehicle while it was still in motion near East Katella and North Wanda Road, according to authorities.

That's when Syed raised a shotgun to his head and fired, killing himself.

Back at the suspected killer's home, at least one neighbor said that he wasn't surprised by what had happened.

"He was just one of those people, you know, that looked like trouble," neighbor Josh Hubner said. "Like when you saw him you should stay away from him."