Mourners packed church pews Tuesday at a memorial service for seven victims slain in a shooting rampage at a small religious college in Oakland, California.

"We realize that at this time we have to draw together, uniting for peace, praying for peace in our city, and praying to stop the violence," said a woman who introduced various parts of the service.

Meanwhile, authorities continued searching for the weapon a gunman used Monday when he killed seven people execution-style at Oikos University.

Accused shooter One Goh gave some details to investigators about Monday's attack, but refused to say where he disposed of the gun, police said.

Investigators had narrowed their search for the weapon and were combing a shoreline park area Tuesday, police spokeswoman Johnna Watson told reporters.

Forensic investigators were still at the scene of the shooting Tuesday, she said.

Police plan to present the case to the district attorney for possible charges sometime this week, she said.

"It's a large investigation. We want to be thorough," she said.

Goh was being held Tuesday in Alameda County's Santa Rita Jail pending an initial appearance in court this week.

The 43-year-old former student at the college "does not appear to be remorseful at all," Oakland Police Chief Howard Jordan said.

Goh told authorities that he was upset about being expelled from Oikos University this year, Jordan said.

Investigators believe Goh walked into the single-story building housing the university Monday morning, took a secretary hostage and went looking for a particular female administrator, who was not there, Jordan told CNN.

Goh took the secretary into the classroom, but when he realized the administrator was not there, he shot her and ordered the students to line up against the wall. Not all of them cooperated, Jordan said, and so he began shooting.

"I'm going to kill you all," the gunman said, according to CNN affiliate KTLA.

"This was a calculated, cold-blooded execution in the classroom," Jordan said. The suspect "just felt a certain urge to inflict pain on them," he said.

After the shooting, the man left the classroom, reloaded his semiautomatic weapon and returned, firing into several classrooms, Jordan said.

He ended his rampage by driving off in a victim's car, police said. In all, seven people were killed and three were wounded.

"This happened within minutes," Jordan said. "We don't think the victims had any opportunity to resist, any opportunity to surrender."

The suspect was arrested a short time after the shooting, when he surrendered to police at a grocery store in the Oakland suburb of Alameda, Jordan said.

Goh offered no resistance when arrested, Jordan said, and was "very cooperative, very matter-of-fact, very calm." Under questioning, Goh "remembered very good details" about the incident, he said.