A former student suspected of opening fire at a small Christian college in California was targeting a school administrator and former classmates who he felt had treated him unfairly.
Seven people were killed and three wounded in the attack at Oikos University in Oakland.
Police chief Howard Jordan said that One Goh, 43, who had been expelled from the college, had been cooperative with investigators after being taken into custody but "not particularly remorseful".
"We know that he came here with the intent of locating an administrator and she was not here," Mr Jordan said.
"He then went through the entire building systematically and randomly shooting victims."
The attack was the deadliest shooting rampage on a US college campus since 32 people were killed by a student at Virginia Tech University in April 2007.
Oikos University is a small Oakland college that has links to the Korean-American Christian community.
Police are still looking for the gun used in the attack, using boats and a robot to search an estuary leading into nearby San Leandro Bay.
Mr Jordan said ballistics evidence showed the weapon was a semi-automatic pistol.
The three wounded victims have all been released from Highland Memorial Hospital in Oakland.
Mr Jordan said those killed included six women and a man, ranging in age from 21 to 40.
The victims came from Korea, Nigeria, Nepal and the Philippines. Six were students and one was a secretary.
He said Mr Goh, a Korean-American, had been expelled from the school two months earlier for "behavioural problems and anger management" issues, but he was not aware of any particular incident that had led to his removal.
"We've learned that the suspect was upset with the administration at the school," Mr Jordan told ABC's "Good Morning America" in an interview.
"He was also upset that students ... in the past when he attended the school, mistreated him, disrespected him and things of that nature," he said.
"We've learned this was a very chaotic, calculated and determined gentleman that came there with specific intent to kill people."
Witnesses said Mr Goh returned to the small college yesterday morning, entered a reception area and opened fire.
He then walked into one of two classes in session, telling former classmates to line up and that he was going to kill them.
Mr Goh, who police said acted alone, surrendered at a Safeway grocery store several kilometres from the college.
