ROSEBURG (United States) • The gunman who killed nine people on a college campus in Oregon was an angry, isolated young man who resented how his life was unfolding, law enforcement officials said.

Police said they had recovered 13 weapons belonging to the suspect, who has been identified by media reports as Chris Harper Mercer, 26.

Six guns, a flak jacket and five rounds of ammunition were found after the rampage at Umpqua Community College in Roseburg, a former timber town about 290km south of Portland.

The rest of the weapons were at the apartment Mercer shared with his mother just outside Roseburg.

US media said the shooter suffered from mental illness and left behind a typed statement several pages long in which he indicated he felt lonely and was inspired by previous mass killings.

"He didn't have a girlfriend and he was upset about that," The New York Times quoted an unnamed senior law enforcement official as having said.

"He comes across thinking of himself as a loser," the official said.

"He did not like his lot in life, and it seemed like nothing was going right for him."

Quiet and withdrawn, Mercer usually deflected neighbours when they asked him how he was doing, or why he always wore the same outfit of combat boots and green army trousers. But there was one subject that got him to open up: guns.

He regularly went to a shooting range with his mother, said neighbours in Torrance, California, where the two lived until moving to Oregon in 2013.

At a barbecue shortly before they left, Mercer spent hours talking with a next-door neighbour 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 neighbour Louie Flores, 32.

"But anything about what was going on in his life, he really didn't say too much at all."

Two years after that fresh start, the authorities said, Mercer carried out the worst shooting rampage in Oregon's history on Thursday morning, killing nine people in the writing class where he was enrolled and wounding others.

Mercer appeared to have had a strong animosity towards organised religion, and some survivors' families have said he asked the victims whether they were Christians before shooting them.

He had used online message boards to express his thoughts about life, including other shootings and the infamy that accompanied the gunmen who carried them out. On a blog post linked to his e-mail address, an Aug 31 entry expressed sympathy for Vester Lee Flanagan II, a television reporter who killed two former colleagues during a live broadcast in Virginia.

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."

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.

Mercer was born in the United Kingdom and arrived in the US as a young boy, his stepsister Carmen Nesnick told CBS Los Angeles.

His parents, Mr Ian Mercer and Ms Laurel Harper, divorced in 2006 when he was a teenager and he continued to live with his mother.

Mercer enlisted in the US Army and served for about a month in 2008 before being discharged for failing to meet administrative standards, military records showed.

He graduated from the Switzer Learning Center in California in 2009. Switzer is a private school geared for special education students, according to its website.

As the investigation continued, officials released the names of the nine people killed: Lawrence Levine, 67, the writing teacher in whose class the shooting took place; and eight students aged between 18 and 59.

Families of the victims expressed their heartbreak at the senseless killings. "Our lives are shattered beyond repair," said the family of Quinn Cooper, 18, who had just started classes at Umpqua after graduating from high school.

Investigators are still piecing together Mercer's actions in the days leading up to the shooting.

A law enforcement official said that police shot and wounded Mercer. But 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.

NEW YORK TIMES, AGENCE FRANCE-PRESSE, REUTERS