Elliot Rodger's roommates had planned to move out of their Isla Vista apartment, one roommate's mother revealed Tuesday.

Jinshuang Liu said that her son, Weihan Wang, had already found another apartment, and planned to move out with the other roommate next semester.

Wang, 20, roommate Cheng Yuan Hong, 20, and a third friend, George Chen, 19, were stabbed to death by Rodger on May 23.

Liu said that her son was a University of California at Santa Barbara computer engineering student who planned on coming home to San Diego for the summer.

She also said that Wang was close to Hong and Chen, but found Rodger's anti-social behavior and late-night music playing disturbing.

"Normally, they don't talk to each other," Liu told NBC San Diego of Wang and Rodger's relationship. "They don't have much interaction."

In Rodger's 141-page manifesto, he wrote that he would have to kill his roommates first in order to "get them out of the way."

Liu and her husband, Charlie Wang, are devastated by the loss of their only child.

"For two days, I was not able to sleep," Liu told NBC. "I still don't know what to do with myself.

"I wish I could go in exchange of my son's life," she continued. "I'm just heartbroken. You just can't imagine for a mom."

Charlie was too overwhelmed with grief to speak to reporters.

Liu said she struggles to understand why her child had to die.

"I'm a strong mom, I'm a nurse, I'm nice to my patients," she said.

"I go to my church a few times a week. I ask God, 'Why doesn't he take me instead of my son?' I don't understand why this happened to me."

After killing three men in his apartment, Rodger went on to fatally shoot two Delta Delta Delta sisters, Katherine Cooper, 22, and Veronika Weiss, 19, outside of their sorority house, and Christopher Michael-Martinez, 20, at a local deli.

After running over bicyclists and pedestrians with his car and engaging in shoot-outs with Santa Barbara police, Rodger committed suicide by shooting himself in the head inside his vehicle.