Students, staff and faculty are evacuated from Umpqua Community College in Roseburg, Oregon, after a deadly at the school on October 1, 2015. (AFP)
Investigators on Saturday tried to piece together evidence on why a 26-year-old gunman went on a shooting rampage at a school in Oregon, killing nine people.
Officials said the gunman, identified as Chris Harper Mercer, was enrolled in the English writing class at Umpqua Community College, where the shooting broke out.
He died following a shootout with police.
Some unconfirmed reports said Mercer was shot and wounded by police but managed to run away and then shot himself.
The Los Angeles Times, quoting local police, said Mercer entered the class around 10:30 am, after it had started, and began firing.
Investigators said 13 weapons belonging to the gunman had been recovered, including six at the school. A flak jacket and five rounds of ammunition were also recovered at the school.
The shooting, the latest in a string of similar attacks in recent years at colleges and schools in the United States, has revived a fierce debate on gun control.
Officials say Mercer had struggled with mental health problems for some time 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 saying.
"He comes across thinking of himself as a loser," the official told the paper.
"He did not like his lot in life, and it seemed like nothing was going right for him."
Another official said the shooter, who lived with his mother, was obsessed with guns and religion and had leanings toward white supremacy.
It was unclear how long he had been a student at Umpqua, a small college of about 3,000 students located in Roseburg, a close-knit rural community.
The rampage took place on the fourth day of the new school year.
Several students said Mercer had also signed up for a theatre class that had not yet started.
Witnesses said he asked his victims their religion before shooting them execution-style.
Passionate about guns
Investigators said they were poring through online postings made by the gunman and examining his computer to try and piece together what set off the rampage.
Mercer moved from Los Angeles to Oregon with his mother in 2013, neighbors said, describing him as withdrawn and quiet but passionate when it came to guns.
"When we talked about guns and hunting, he was real open about it," Louie Flores, 32, a neighbor from California, told the Times.
"But anything about what was going on in his life, he really didn't say too much at all."
In online postings linked to Mercer's email address, investigators reportedly found one entry in which he expressed sympathy for a dismissed television reporter who killed two former colleagues during a live broadcast in Virginia in August.
In Roseburg, residents tried to come to terms with the tragedy and the sad reality that their town would now be remembered as the site of a mass killing.
The bodies of the nine victims - five women and four men aged between 18 and 67 - were handed back to their families on Friday.
Nine other people were injured in the rampage, including one woman who was shot in the head, officials said.
Chris Mintz, 30, an army veteran, had tried to stop the bloodshed by charging Mercer but was shot seven times while pleading that it was his son's sixth birthday. He survived.
The mass shooting reflects a grim reality of American life, with similar incidents happening on a regular basis.
The last mass shooting at a US school took place in 2012 when 20 elementary school students and six adults were killed at Sandy Hook Elementary School in Connecticut.
According to data compiled by the group Everytown for Gun Safety, there have been 142 school shootings in the United States since the Sandy Hook massacre.