ROSEBURG, Ore. -- The gunman who killed nine people at an Oregon community college said in writings he left behind that everyone else was "crazy" and ranted about not having a girlfriend, a law enforcement official said Monday.
The official also said the mother of 26-year-old gunman Christopher Harper-Mercer has told investigators he was struggling with some mental health issues. The official is familiar with the investigation but wasn't authorized to speak publically because it is ongoing.
Harper-Mercer complained in writings about not having a girlfriend, and he seemed to feel like he was very rational while others around him were not, the official said.
He wrote something to the effect of: "Other people think I'm crazy, but I'm not. I'm the sane one," the official said. The writings were a couple of pages long.
The New York Times reported that Harper-Mercer's mother, Laurel Harper, was an avid gun enthusiast. According to the newspaper, she wrote online about keeping multiple guns at home and said that both she and her son had expertise in using firearms.
Also Monday, some faculty, staff and students returned to the campus for the first time since the shooting, while President Barack Obama announced he will travel to Oregon to visit privately with victims' families.
Classes do not resume at Umpqua Community College until next week, but some students came to the campus to pick up belongings they left behind Thursday when they fled. Others met with professional groups to discuss their trauma and grief.
A memorial was growing on the driveway leading to Snyder Hall, where Harper-Mercer opened fire. Besides those who died, nine people were wounded. Harper-Mercer killed himself after a shootout with police.
"It was hard not to focus on Snyder Hall," student Joel Mitchell said. "When we got back, I think a lot of people were probably ... looking at it, checking it out, seeing what it looked like."
When classes resume next week, Shannon Dietz will be back, even though her mother, Kim, also a student, was killed in the shooting.
"I won't think of it as the place where there was this shooting," Shannon told CBS News correspondent John Blackstone. "I'll think of it as the place where my friends are."
A group of eight held hands and bowed their heads in prayer in front of the building. Elsewhere, clusters of people chatted at picnic tables or near buildings.
In a courtyard near the center of campus, a therapy dog sat on a blanket with its handler. A woman, crouched down, wiped away a tear.
"I needed to be here," student Madysen Sanchez said. "I needed to come and see my friends, make sure they're OK."
At least one student injured in the shooting was among those who returned Monday, college President Rita Cavin said. She did not identify the student.
Chaplains who had been on campus said they were both helping with and participating in the healing process.
"I'm going through the grieving process myself because this has touched everyone in the community," chaplain Russell Wilson said. "If you don't know someone that goes here, you know someone that knows someone."
Meanwhile, Obama said he will visit Roseburg on Friday as he opens a four-day trip to the West Coast. No additional details about his visit were immediately available.
Obama has renewed his call for stricter gun laws following the shooting and has expressed exasperation at the frequency of mass shootings in the U.S.