A Korean-American former student at a California religious college lined up his victims and shot them them execution-style, police said Tuesday.
Police were holding the suspect in the fatal shootings of seven people Monday at Oikos University in Oakland which stunned the tightly knit Korean American community in the area.
"This was a calculated, cold-blooded execution in the classroom," Oakland police chief Howard Jordan told CNN.
Details of the shooting and the victims emerged a day after the ethnic Korean gunman allegedly walked into a building housing Oikos University, took a receptionist hostage and then sought out a particular female administrator.
When he realized the administrator was not in the building, he shot the secretary and then lined students up against a wall and shot them one by one, Jordan told CNN.
"I'm going to kill you all," the gunman allegedly told the students.
Six women and a man -- all students at the school, aged 21 to 40 -- were killed in the rampage. Jordan said they were from Nigeria, Nepal and Korea.
"This happened within minutes," Jordan said. "We don't think the victims had any opportunity to resist, any opportunity to surrender."
The gunman then walked out of the classroom, reloaded his automatic weapon, and fired into several classrooms before driving off in a victim's car to neighboring Alameda, California, he said.
He said the gunman then called his parents and surrendered to police who arrived on the scene.
Identified as 43-year-old One Goh, the suspect was a former student at the Christian college and complained to police that he had been treated disrespectfully by staff members, Jordan said.
"He was having some behavioral problems at the school and was asked to leave several months ago," Jordan said in a separate interview with ABC television, adding that he was cooperating with investigators.
"We've learned this was a very chaotic, calculated and determined gentleman that came there with the specific intent to kill people," Jordan said.
Some 35 people were in or near the building at the time. Of those, 10 were hit and five were pronounced dead at the scene. Two others died later in hospital. Survivors were found hiding in locked and darkened rooms.
"No American mayor wants to have this situation," Oakland Mayor Jean Quan told reporters. "It seems that in the last decade we've gotten used to seeing senseless mass killings like this... This has been a terrible tragedy."
She said the city was trying to recruit more Korean-speaking grief counselors, saying the shooting "will leave the community asking questions for a long time."
A memorial service was to be held at 6:00 pm (2200 GMT) Tuesday.
The Oakland Tribune reported that the suspect's brother, US Army Sergeant Su Wan Ko, died in a traffic accident in Virginia in March 2011 while on special assignment from a research institute in Germany.
One Goh reportedly attended the memorial service.
South Korea's Yonhap news agency, citing officials at the South Korean consulate in San Francisco, identified the shooter as Ko Won-Il, a US citizen of Korean descent.
Police described the suspect as "male, Asian, heavy build, khaki clothing."
Lisa Resler, 41, said she was leaving the Safeway supermarket in Alameda with her daughter when she saw store security confronting a young Asian man, whom she described as looking "very sedated" as he was handcuffed.
Within minutes of the mid-morning shooting, SWAT teams took up position around the building, some smashing glass with sledgehammers and rushing inside as officers helped students evacuate, the San Francisco Chronicle reported.
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 wounded woman said the shooter was a man in her nursing class who rose up and shot one person in the chest, then began firing wildly in the classroom, Johnson told the Chronicle.
"She said he looked crazy all the time," Johnson said, quoting the victim. "But they never knew how far he would go."
The female victim "had a hole in her right arm the size of a silver dollar with blood coming down," Johnson said.
The school, which offers degrees in nursing, biblical studies and Christian ministry, says "students are given the opportunity to obtain a Christian education that is based on solid Christian doctrine and ideology.