When a downstairs neighbour of Laurel Harper learned there was a gunman on the loose at Umpqua Community College, he ran up to tell her, knowing that her son, Christopher Harper-Mercer, was a student there. Like other parents, Harper started to set out in desperate search for her son, fearing he could be hurt.

“She was very upset,” said the neighbour, who asked not to be named, citing his family’s privacy. But as she was leaving, the local sheriff and his deputies intercepted her and broke the news that her son was the gunman.

Harper, who divorced her husband a decade ago, appears to have been by far the most significant figure in her son’s troubled life; neighbours say he rarely left their apartment. Unlike his father, who said on television that he had no idea Harper-Mercer cared so deeply about guns, his mother was well aware of his fascination. In fact, she shared it: in a series of online postings over a decade, Harper, a registered nurse, said she kept numerous firearms in her home and expressed pride in her knowledge about them, as well as in her son’s expertise on the subject.

She also opened up about her difficulties raising a troubled son, who used to bang his head against the wall, and said she and her son struggled with Asperger’s syndrome, an autism spectrum disorder. She tried to counsel others whose children faced similar problems. All the while, she expressed hope that her son could lead a successful life in finance or as a filmmaker.

Harper did not respond to messages seeking comment. In an online forum, answering a question about state gun laws several years ago, Harper took a jab at “lame states” that impose limits on keeping loaded firearms in the home, and noted that she had AR-15 and AK-47 semiautomatic rifles, along with a Glock handgun. She also indicated that her son, who lived with her, was well versed in guns, citing him as her source of information on gun laws, saying he “has much knowledge in this field”.

“I keep two full mags in my Glock case. And the ARs & AKs all have loaded mags,” Harper wrote. “No one will be ‘dropping’ by my house uninvited without acknowledgement.”

Law enforcement officials have said they recovered 14 firearms and spare ammunition magazines that were purchased legally either by Harper-Mercer (26), or an unnamed relative. Harper-Mercer had six guns with him when he entered a classroom building last Thursday and started firing on a writing class in which he was enrolled; the rest were found in the second-floor apartment he shared with his mother.

TweetyBird

Harper’s posts were found on Yahoo Answers, a site where she spent countless hours over the past 10 years, mostly answering medical questions from strangers, occasionally citing her own difficulties raising a troubled child. Her Yahoo profile had a user name of TweetyBird, accompanied by a cartoon image of a nurse. In many of her postings, she included her email address, which public records link to Harper.

Harper and Christopher's father, Ian Mercer of Tarzana, California, divorced in 2006 and were separated years earlier. Mercer told CNN last week that he thought the nation should change its gun laws, saying the massacre "would not have happened" if his son had not been able to buy so many handguns and rifles.

Neighbours in southern California have said Harper and her son would go to shooting ranges together, something Harper seemed to confirm in one of her online posts. She talked about the importance of firearms safety and said she learned a lot through target shooting, expressing little patience with unprepared gun owners: “When I’m at the range, I cringe every time the ‘wannabes’ show up.”

In addition to talking about guns, Harper (64) was a prolific commenter in online forums dealing with medical issues, frequently answering questions from strangers with a tone of empathy and concern. She expressed having expertise in autism, saying that both she and her son – whom she never identified by name – had Asperger’s syndrome.

Consoling another parent seeking help with disruptive behaviour by an autistic child, Harper said her son “was, among other things, a head-banger” when he was younger and was initially misdiagnosed with attention deficit disorder. But over time, he had learned to cope and was doing better, she wrote: “I was in your shoes and now my son’s in college.”

She expressed frustration with people who questioned how successful a person with autism could be, noting: “I have Asperger’s and I didn’t do so bad. Wasn’t easy (understatement) but it can be done.” She also said she had “dealt with it on a daily basis for years and years” because of her son, who she said was progressing well.

“He’s no babbling idiot nor is his life worthless,” Harper wrote. “He’s very intelligent and is working on a career in filmmaking. My 18 years worth of experience with and knowledge about Asperger’s syndrome is paying off.”

Confided difficulties

Alexis Jefferson, who worked with Harper at a southern California subacute care centre around 2010, said the gunman’s mother sometimes confided the difficulties she had in raising her son, including that she had placed Harper-Mercer in a psychiatric hospital when he did not take his medication.

“She said that my son is a real big problem of mine,” Jefferson said in a telephone interview. “She said, ‘He has some psychological problems. Sometimes he takes his medication, sometimes he doesn’t. And that’s where the big problem is, when he doesn’t take his medication.’”

Jefferson said Harper had described bringing her son to the Del Amo Behavioral Health System in Torrance, California, near where they had lived before moving to Oregon. "He calls and says, 'Take me out, take me out,'" Jefferson said, recalling her conversations with Harper. "She didn't take him out until the doctor said he was ready to get out."

Neighbours in the apartment building where the mother and son lived said Harper-Mercer rarely strayed far. They would see him getting the mail or walking down the road to buy a soda at a nearby market, but said he did not appear to have a job in Roseburg and stayed home most of the day.

At night, when his mother went to her nursing jobs, a neighbour whose bedroom was directly below Harper-Mercer’s said she frequently heard him pacing until three or four in the morning. She complained to her own family about the noise, but never mentioned it to Harper-Mercer or his mother.

In an interview in their ground-floor apartment, the neighbour, a young woman, and her mother echoed other people’s memories of Harper-Mercer as quiet and distant. They said Harper occasionally invited them upstairs for a visit, or when she was writing a complaint letter to the apartment managers about the smell of marijuana smoke or late-night guests at another neighbour’s apartment. She would ask her son to say hello, but he rarely chatted with them.

“Chris would just be in his room,” the young woman said.

Nursing studies

The young woman’s mother, who immigrated from the Philippines, said she shared Filipino meals with Harper, and Harper taught her how to drive. She wrote a letter of support when Harper was applying for a $1,500 scholarship to continue her nursing studies. The family still has Harper’s thank-you card.

“Once again, thank you so very much for helping me with my scholarship application,” the note says. “Now I can attend the nursing program without having to stress out about tuition!”

The day of the shooting, the young woman from downstairs rushed home to check on her toddler, and saw Harper standing outside talking with the police. It was Harper’s son who had killed nine people and wounded several others before exchanging fire with the police and then taking his own life.

“She was still in denial of it,” the young woman said. “She just handled it like a nurse would – like it was another person’s life.”

New York Times service