SANTA MONICA, California (CNN) -- Six people were killed in a shooting rampage in Santa Monica, California, that ended Friday with the gunman clad in tactical gear dead in a college library and a "person of interest" in custody, authorities said.
"We are not convinced 100 percent that the suspect who was killed operated in a solo or alone capacity," Santa Monica Police Chief Jacqueline Seabrooks told reporters.
The comments came as police and firefighters searched the sprawling campus of Santa Monica College for other possible victims or shooters. By early evening, authorities declared the campus clear.
The gunman has not been identified by authorities, Seabrooks said. She described him as a white male between the age of 25 and 35, clad in black and wearing what appeared to be a ballistic vest.
Seabrooks did not identify the person in custody, nor did she explain why authorities wanted to talk to him.
At least three people were wounded in the shootings, which authorities believe began with a house fire and gunshots shortly before noon in a residential neighborhood near the college.
The gunman carjacked a woman, said Jerry Cunningham, who looked out her window after hearing shots fired.
She saw the gunman, and a neighboring house on fire.
The gunman then waved another car by, she said. That driver, a woman, hesitated for just a moment, and the gunman "fired three shots directly into her and the car," Cunningham said. It is not known if that motorist was wounded or dead.
Inside the house, firefighters found the bodies of at least two people, Seabrooks said.
Investigators believe the gunman knew the dead people in the house, but police were unsure of the connection.
The others killed in the rampage were targeted randomly, Seabrooks said.
It was not immediately clear whether a woman who died from wounds at Ronald Reagan UCLA Medical Center was counted among the six deaths. Another woman wounded in the shooting remains in critical condition, Dr. Marshall Morgan, the chief of emergency medicine at the medical centerm said Friday evening..
Within minutes of the carjacking, authorities said, the gunman targeted a bus in Santa Monica. Two passengers were injured, Suja Lowenthal, a Big Blue Bus spokeswoman, told CNN.
A short distance later, the gunman opened fire on cars, including a patrol car, adjacent to the college.
"There was an exchange of gunfire at the time, and the suspect tried to evade," Seabrooks said.
The gunman ran on to the campus, where he again exchanged gunfire with police.
Student Joe Orcutt saw the exchange of gunfire and fled, only to come face-to-face later with the gunman near the campus parking lot.
"He was standing there. He looked over at me, and I looked at him. He just panned his gun and trained it on me, and I just jumped behind the building and he shot at me," Orcutt said.
Orcutt said he heard bullets "whiz by my head."
The gunman was "very calm, not running around." He was just "looking around for targets very casually," he said.
"He just looked like he was standing there posing for the cover an ammo magazine or something. It was bizarre."
The gunman exchanged gunfire at least once on the campus with police, Seabrooks said.
As he fled toward the campus library, he shot a woman, she said.
A number of students were in the library building studying for finals when the gunman burst in. More than 30,000 students are enrolled in the two-year community college.
A woman -- who was shaken up by the ordeal and asked not to be identified -- said she was in the building when she heard a noise, realized it was a gunshot, then took off running.
Then, in a hallway, she saw a dark-haired man whom she initially mistook for a police officer but later realized was the shooter. The man -- who she said was wearing black combat boots and what appeared to be a bullet-proof vest -- was quiet and walking casually.
"(He had) a big shotgun," the woman said.
She and a colleague eventually realized something wasn't right and ran in the opposite direction. "Multiple" gunshots rang out at one point, in an exchange of gunfire the woman described as like a war zone.
Priscilla Morales, who was also studying in the library, told CNN she looked out the window and saw people running.
She and her friends grabbed their books and belongings to leave the study room. "As we open the door, we hear three gunshots," she said.
Morales and the others closed the door and hid.
Still, she could hear the commotion: gunshots and then the gunman screaming.
Morales also said she heard police tell the gunman to "drop it."
"I was so scared and thought literally I was going to die," she said.
President Barack Obama was in Santa Monica
CNN's Miguel Marquez reported from Santa Monica and Chelsea J. Carter and Phil Gast reported and wrote from Atlanta. CNN's Cheri Mossburg and Traci Tamura contributed to this report.