ROSEBURG, Ore. — Christopher Harper-Mercer was withdrawn and quiet as he grew up in southern California, spending most of his time indoors at his mother’s apartment and deflecting neighbors when they asked him how he was doing, or why he always wore the same outfit of combat boots and green Army pants. But there was one subject that got him to open up: guns.
Mr. Harper-Mercer collected handguns and rifles, and he regularly went to a shooting range with his mother, said neighbors in Torrance, Calif., where the two lived until moving to Oregon in 2013. At a barbecue shortly before they left, Mr. Harper-Mercer spent hours talking with a next-door neighbor about guns and how he and his mother were excited to leave Los Angeles and get a fresh start.
“When we talked about guns and hunting, he was real open about it,” said the neighbor, Louie Flores, 32. “But anything about what was going on in his life, he really didn’t say too much at all.”
But two years after that fresh start, the authorities say, Mr. Harper-Mercer, 26, carried out the worst shooting rampage in this state’s history at Umpqua Community College on Thursday morning, killing nine people in the writing class where he was enrolled and wounding others. He was armed with six guns, a flak jacket and spare ammunition magazines, suggesting he expected a long siege. He had seven more guns at his apartment, officials said.
For investigators searching for his path to mass murder, he left behind a typewritten manifesto at the scene and a string of online postings that showed he had become increasingly interested in other high-profile shootings, angry at not having a girlfriend and bitter at a world that he believed was working against him.
Mr. Harper-Mercer appeared to have a particular animus against organized religion, and some survivors’ families have said he asked the victims whether they were Christians before shooting them.
Just this week, on Tuesday, using the handle lithium_love, he commented on a post titled “How many girlfriends have you had?” by saying “0. Never had anyone.” When pressed further by another user, he responded “Well, it means I’ve never been with anyone, no woman nor man (nor dog or animal or any other).” Then, on Wednesday, responding to a comment that he “must be saving himself for someone special,” he said, “Involuntarily so.” It was a day before the killings.
“He did not like his lot in life, and it seemed like nothing was going right for him,” a law enforcement official said, describing the writings found at the crime scene. “It’s clear he was in a very bad state of mind.”
Graphic | What Happened in the Oregon Community College Shooting A gunman opened fire on a teacher and students on Thursday morning at Umpqua Community College in Roseburg, Ore.
He retreated to online message boards to express his thoughts about commercialism, other shootings and the infamy that accompanied the gunmen who carried them out. On a blog post linked to Mr. Harper-Mercer’s email address, an Aug. 31 entry expresses sympathy for Vester Lee Flanagan II, a dismissed television reporter who killed two former colleagues during a live broadcast in Roanoke, Va.: “I have noticed that people like him are all alone and unknown, yet when they spill a little blood, the whole world knows who they are.”
The entry continues, “Seems the more people you kill, the more you’re in the limelight.”
After his parents divorced when he was about 16, he lived with his mother, Laurel Harper, a nurse who fiercely protected him from, among other things, the neighborhood sounds of loud children and barking dogs. Once, neighbors said, she went door to door with a petition to get the landlord to exterminate cockroaches in her apartment, saying they bothered her son.
“She said, ‘My son is dealing with some mental issues, and the roaches are really irritating him,’ ” Julia Winstead, 55, said. “She said they were going to go stay in a motel. Until that time, I didn’t know she had a son.”
He was listed as a 2009 graduate of the Switzer Learning Center in Torrance, a private school for students with learning disabilities, emotional issues and other special-education needs. Officials from the school declined to comment on Friday. Mr. Harper-Mercer joined the Army for a month in 2008 but was discharged before finishing basic training.
Rosario Lucumi, 51, rode the same bus in Torrance as the young man when she went to work. She said he always wore earphones and listened to music on the rides. She said he and his mother lived for less than a year in a small one-bedroom apartment in Torrance. “They were always together,” she said.
His parents struggled financially over the years, filing for bankruptcy in 1992, and his father, Ian Mercer, filed again in 2002. California records show that Ms. Harper had been a licensed vocational nurse. She is now a licensed practical nurse in Oregon. She apparently contributed to online forums dealing with health issues. In one exchange, a writer who appeared to be Ms. Harper offered assistance to the mother of a child with Asperger’s syndrome, saying, “I’m a nurse and also have an Aspergers kid.”
Neither of his parents could be reached for comment, but his father told television reporters outside his California home on Thursday night that he was shocked by the events.
Interactive Feature | Mass Shootings in the U.S. This partial list dates to 2007, the year of the deadliest mass shooting in U.S. history.
Mr. Harper-Mercer appeared to have sought community on the Internet, leaving hints behind of his passions, his loneliness, his likes and dislikes. A picture of him holding a rifle appeared on a MySpace page with a post expressing a deep interest in the Irish Republican Army. It included footage from the conflict in Northern Ireland set to “The Men Behind the Wire,” an Irish Republican song, and several pictures of gunmen in black balaclavas.
A dating profile published more than three months ago with his email address on the website Spiritual Passions, and featuring photos of Mr. Harper-Mercer, appeared to broaden the portrait. “Looking for someone who shares my beliefs, and is similar to me,” it said. It said he enjoyed horror movies, and under hobbies, it listed “killing zombies” along with the “Internet” and other pursuits.
The profile described Mr. Harper-Mercer as “Not Religious, Not Religious, but Spiritual,” and it said he belonged to a group called “Doesn’t Like Organized Religion.”
On a file-sharing forum where illicit content is often shared, blog posts linked to his email address expressed sympathy for Mr. Flanagan, who killed two former co-workers in August.
“People like him have nothing left to live for, and the only thing left to do is lash out at a society that has abandoned them,” the user wrote days after the Roanoke shooting. “His family described him as alone, no partner/lover. A victim not only of his own perception but also of our social media soaked environment.”
In a post published in September, after the shooting death of Darren Goforth, a suburban Houston police officer, at a gas station, the user with Mr. Harper-Mercer’s email address said it was the inevitable result of the Black Lives Matter movement. “In case anyone’s wondering, I’m not on the side of the suspect, I’m on the side of the officer, and generally don’t agree with the black lives matter protests,” the user said.
The user, who posted under the name lithium_love, shared pornography, as well as movies like “Illuminati Secrets” and “UFO Secrets of the Third Reich.”
Bryan Clay, 18, a neighbor from Torrance, said he once asked Mr. Harper-Mercer why he wore “a military get-up” every day.
“He kind of just didn’t want to talk about it” and changed the subject, Mr. Clay said.
“He didn’t say anything about himself,” he added.
Derrick McClendon, 42, another former neighbor, said Mr. Harper-Mercer was so timid and ill at ease that on occasion Mr. McClendon would ask him if something was wrong.
“I would say, ‘Hey, man, you all right?’ ” Mr. McClendon said. “He would say, ‘Hi,’ but that’s it. He was really shy.”
Rosario Espinoza, 33, was once a neighbor and moved into the apartment that the mother and son shared when the two moved from Torrance a couple of years ago. She said that the two “kept to themselves,” but that from time to time Mr. Harper-Mercer’s mother would complain that Ms. Espinoza’s young children were playing too loudly and bothering her son.
“They’re normal children that play, but she would get really upset,” Ms. Espinoza said. “It was during the daytime. But I guess the noise would really upset him, the son.”
One night, the Flores family, the next-door neighbors, were watching a movie when Mr. Harper-Mercer knocked on the door.
“He said: ‘Can you turn that down? Your TV is really loud,” Esther Flores said. “And he just had that look. No smile, nothing. And he just turned and walked away. My husband didn’t even have a chance to respond.”
Other neighbors said the mother would confront them about their barking dogs when they returned from work. “She would wait till they got home and knock on their door,” Kim Hermenegildo, 48, said.
Ms. Espinoza said that she heard Mr. Harper-Mercer’s mother got a job in Oregon, prompting the family’s move north.
In Winchester, Ore., Mr. Harper-Mercer and his mother shared an apartment in a dun-colored building that sat roped off behind police tape on Thursday evening, guarded by sheriff’s deputies who shooed away reporters.
Bronte Hart, a neighbor who said she lived in an apartment below Mr. Harper-Mercer’s, described a more assertive young man than his former neighbors in California did. Far from avoiding social interaction, she said, he frequently shouted at her for smoking on her balcony.
“He yelled at us, me and my husband,” said Ms. Hart, who lives with her husband and father. “He was not a friendly type of guy. He did not want anything to do with anyone.”
Investigators are still piecing together Mr. Mercer-Harper’s conversations and actions in the days leading up to the shooting. But that path ended at Snyder Hall at 10:30 a.m., when he shot his way into his classroom and, according to some, interrogated his classmates about their faith as he killed them. When the police reached Mr. Harper-Mercer, they shot and wounded him, a law enforcement official said. He was able to run away and then shot himself. He died in the ambulance en route to the hospital. It was not clear which shot was the fatal one.
Correction: October 2, 2015
An earlier version of this article misstated the professional background of Laurel Harper, the mother of Christopher Harper-Mercer. She had not been licensed as a registered psychological assistant in California, and she is a licensed practical nurse in Oregon, not in California.
Jack Healy reported from Roseburg, and Ian Lovett from Torrance, Calif. Liam Stack and Michael S. Schmidt contributed reporting from New York, and Dirk VanderHart from Roseburg.