Eyewitnesses have described the distressing moments when the gunman started firing shots at a California religious college, where seven people were killed.
Angie Johnson, 52, said she saw a young woman leaving the building with blood coming from her arm and crying, "I've been shot, I've been shot."
The woman said the shooter was a man in her nursing class who rose up and shot one person at point blank range in the chest before he started spraying the room with bullets, Johnson said, cited by the Chronicle.
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"She said he looked crazy all the time," Johnson said the victim told her. "But they never knew how far he would go."
The victim "had a hole in her right arm the size of a silver dollar with blood coming down," she added.
The motive for the shootings was unclear, said Oakland City Council president Larry Reid, who had been briefed by Oakland's chief of police.
"There are seven (families) now that are having to deal with this horrendous act," Mr Reid told CNN, after the shooting at Oikos University in East Oakland.
"Our police department right now is doing their work and trying to understand what in fact was his motive to come and take the lives of seven individuals, and then also to leave three individuals wounded," Reid said.
"That information will come out during the legal process that he now finds himself in," he said.
Initially police warned that a suspect, described as Korean and in his 40s, was at large, but a short time later, the Oakland Police Department said on Twitter that they had a "possible suspect in custody."
"No imminent public safety threat appears to exist in immediate area," it added.
The suspect was arrested some five miles (eight kilometers) away outside a Safeway supermarket in Alameda, according to the Oakland Tribune, which cited a witness as saying the suspect was calm as he was taken into custody.
Lisa Resler, 41, said she was leaving the Alameda store with her daughter when she saw a young Asian man wearing a hat being confronted by store security. She described him as looking "very sedated" as he was handcuffed.
Within minutes of the mid-morning shooting, SWAT teams took position around the building, some smashing glass with sledgehammers and rushing inside as officers helped students evacuate the campus, the Chronicle reported.
