Oregon shooting
A sign at the edge of campus welcomes students and staff back to Umpqua Community College, Oct. 5, 2015, in Roseburg, Oregon. Getty Images/Scott Olson

Chris Harper-Mercer, the shooter behind the deadly rampage at Umpqua Community College in Roseburg, Oregon, ranted about not having a girlfriend in a manifesto, media reports said. The 26-year-old opened fire in the community college Thursday, killing nine people.

Harper-Mercer detailed his grievances about not having a girlfriend and everyone around him being “crazy,” a law enforcement official said, according to the Associated Press (AP). He also reportedly wrote in the manifesto that he felt like he was very rational. The official, who was not authorized to speak about the investigation, also said that Harper-Mercer’s mother told authorities that her son was struggling with some mental health issues.

"Other people think I'm crazy, but I'm not. I'm the sane one," Harper-Mercer wrote, according to the official.

The news of the manifesto comes after Oregon pastor Randy Scroggins said Sunday that his daughter, who survived the shooting, told him that the gunman gave an envelope with a flash drive to a student whom he spared. Harper-Mercer reportedly asked the student to hand it over to police.

On Monday, the campus opened for students and staff, but classes will not resume until next week.

"It was hard not to focus on Snyder Hall," student Joel Mitchell said, according to AP. "When we got back, I think a lot of people were probably ... looking at it, checking it out, seeing what it looked like."

Harper-Mercer stormed his writing class in Snyder Hall, where he shot and killed his professor and several classmates. He reportedly ordered individuals to stand, asked them their religion and then started shooting them. He committed suicide soon after officers arrived on the scene and exchanged fire with him.

President Barack Obama reportedly announced that he will travel to Oregon Friday to meet the victims’ families.

Investigators interviewed Harper-Mercer’s mother, with whom he lived in an apartment few miles from the college. Authorities have so far seized 14 guns that were either with him or recovered from his home.

Over the past several years, Harper-Mercer’s mother reportedly posted on websites about the difficulties of having a son with Asperger's syndrome, a form of autism.