One Goh, 43, has been charged with killing seven people and wounding three others earlier this month at Oikos University. The 43-year-old has not yet entered a plea.
In an exclusive jailhouse interview with a local San Francisco TV station, he said he realizes the victims' relatives are "so angry with me."
"(But) if I tell them sorry, it doesn't bring anybody back," he said.
As they spoke, Goh kept his head down, the reporter said. His eyes were bloodshot and at one point he started to cry.
Goh told the reporter that he only remembers parts of the day the shooting took place, and said, "You never know what you will do one day or what your mind will do."
The South Korean native did not appear to make any effort to dispute allegations by authorities that he was the gunman on April 2 at Oikos University.
Police have said Goh was targeting an administrator who had been involved in his financial dispute with the school. When he learned she wasn't there, police say, he began shooting in classrooms.
The Associated Press contributed to this report.