A Korean-American former student accused of killing seven people at a private Christian college in California lined up his victims and shot them execution-style, police said Tuesday.
The 43-year-old planned the killings after being expelled from the college near San Francisco, was "upset" at staff and other students and had displayed "no remorse," a senior officer said.
Police were holding the suspect in the fatal shootings that took place 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.
The suspect, identified here as One Goh and by South Korea's Yonhap news agency as Ko Won-Il, opened fire with a .45 caliber handgun, according to local media reports.
"We learned from the suspect and witnesses he was distraught because he was picked on ... He planned (the attack) several weeks in advance," Jordan told the local Fox affiliate KTVU.
Goh had difficulty speaking English, he said, adding: "He was so upset he went out and purchased a weapon and had every intent to kill people yesterday." Although cooperating with officers, "he has not shown any remorse," he added.
As well as the massacre scene, investigators focused Tuesday on a location a few miles away where they were searching "for firearm, believed to have been used and discarded yesterday by suspect," according to the police Twitter feed.
Details of the shooting emerged a day after the 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.
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.
Oakland Mayor Jean Quan 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 Tuesday (0100 GMT Wednesday).
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.
The shooting suspect reportedly attended the memorial service.
The college where the shootings took place offers degrees in nursing, biblical studies and Christian ministry. Its website says "students are given the opportunity to obtain a Christian education that is based on solid Christian doctrine and ideology.
In a sign of jitters sparked by the shooting, police briefly locked down a school some four miles (six kilometers) away after "multiple shots" were reported, but lifted the order shortly after, police said on Twitter.