Harper-Mercer's mother allowed her troubled son to have guns and acknowledged in online posts that he struggled with a mild form of autism, but she didn't seem to know he was potentially violent.
The online writings by Laurel Harper date from a year ago to nine years ago. She and Harper-Mercer shared an apartment outside Roseburg. Investigators have recovered 14 firearms - six found at the college and eight at the apartment.
In her online postings, Laurel Harper talked about her love of guns and her son's emotional troubles, but there are no hints of worry that he could become violent.
While living in California, Harper-Mercer graduated from a learning center for students with learning disabilities and emotional problems. His parents divorced when he was a teenager and he lived with his mother.
Harper-Mercer's social media profiles suggested he was fascinated by the Irish Republican Army and frustrated by traditional organized religion.
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."