(Reuters) - The gunman who police suspect killed seven people and wounded three at a Christian college in Oakland, California, was upset with the school's administration and students over what he viewed was unfair treatment while he was enrolled there, the Oakland police chief said Tuesday.

Oakland Police Chief Howard Jordan said ABC's "Good Morning America" that One Goh, 43, has been cooperating with investigators trying to piece together a motive for killings at Oikos University. It was the deadliest shooting rampage on a U.S. college campus since 32 people were killed at Virginia Tech University in April 2007.

"We've learned that the suspect was upset with the administration at the school," Jordan said. "He was also upset that students ... in the past when he attended the school, mistreated him, disrespected him and things of that nature.

"We've learned this was a very chaotic, calculated and determined gentleman that came there with specific intent to kill people," Jordan said.

Witnesses say Goh, a Korean-American who had recently been removed as a student from Oikos, returned to the small college on Monday 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.

Goh, who police say acted alone, surrendered at a Safeway grocery store several miles from the college, which has links to the Korean-American Christian community.

"He was having, we believe, some behavioral problems at the school and was asked to leave several months ago," Jordan said.

Police expect to deliver the results of their investigation to prosecutors, who will decide what charges to file, on Wednesday.

STUDENTS THOUGHT SHOOTER WAS JOKING

Paul Singh, whose 19-year-old sister Devinder Kaur was shot in the arm during Monday's rampage, told Reuters that according to his sister Goh had not been seen at the college in several months. When he burst into her classroom, he ordered the students to line up against a wall.

"'Get in line and I'm going to kill you all,' is what he said this morning, my sister told me. They thought he was joking at first,'" Singh said.

Tashi Wangchuk said his wife, Dechen Yangzom, 28, was in another classroom when she heard gunfire.

"Out of instinct, she locked the door and turned off the lights. Then the guy came and banged on the door and shot several rounds at the door and then he left," Wangchuk said. "The police said what she did was heroic."

The Oikos killings came just about a month after a student opened fire at a high school in Chardon, Ohio, killing three students and wounding two.

Images from local television stations showed a chaotic scene at Oikos on Monday. Frightened students and staff ran from the school, located in a light industrial area near Oakland International Airport, as police and SWAT teams carrying assault rifles surrounded the area.

Oikos, which offers programs in theology, nursing, music and Asian medicine, describes itself on its website as having been started to provide the "highest standard education with Christian value and inspiration."

(Writing by Dan Burns; Additional reporting by Deborah Zabarenko, Dan Whitcomb, Mary Slosson, Emmett Berg and Ronnie Cohen; Editing by Bill Trott)