The 26-year-old gunman who opened fire on fellow students in his college English class, killing nine people, was an army boot camp dropout who studied mass shooters before becoming one himself.
A day after the rampage in Oregon timber town of Roseburg, the authorities said Chris Harper-Mercer wore a flak jacket and brought at least six guns and five ammunition magazines to Umpqua Community College.
Investigators found another seven guns at the apartment he shared with his mother.
Officials released the names of the dead, who ranged in age from 18 to 67 and included several teenagers and a teacher.
One of the students was active in the Future Farmers of America and loved to play football. Another was on only his fourth day of college. One was a 59-year-old student whose daughter was enrolled in the same school but not injured in the shooting.
Grieving families began sharing details of their loved ones.
“We have been trying to figure out how to tell everyone how amazing Lucas was, but that would take 18 years,” the family of Lucas Eibel said.
The teenager, who was studying chemistry, volunteered at a wildlife centre and animal shelter.
Quinn Glen Cooper’s family said their son had just started college and loved dancing and voice acting.
“I don’t know how we are going to move forward with our lives without Quinn,” the Coopers said. “Our lives are shattered beyond repair.”
Seven other people were wounded in the attack in Roseburg, about 180 miles south of Portland.
Harper-Mercer, who died during a shoot-out with police, was armed with handguns and a rifle, some of which were military grade.
The weapons had been purchased legally over the past three years, some by him, others by relatives, said Celinez Nunez, assistant field agent for the Seattle division of the Bureau of Alcohol, Tobacco and Firearms.
Oregon’s senior prosecutor said the shooter used a handgun when he opened fire on classmates and stashed a rifle in another room and did not fire it.
Those who knew the shooter described an awkward loner.
At a block of flats where Harper-Mercer and his mother had lived in Southern California, neighbours remembered a quiet and odd young man who rode a red bike everywhere.
Reina Webb, 19, said the man’s mother was friendly and often chatted with neighbours, but Harper-Mercer kept to himself.
She said she occasionally heard him having temper tantrums in his flat.
“He was kind of like a child so that’s why his tantrums would be like kind of weird. He’s a grown man. He shouldn’t be having a tantrum like a kid. That’s why I thought there was something – something was up,” she said.
Harper-Mercer’s social media profiles suggested he was fascinated by the Irish Republican Army and frustrated by traditional organised religion.
He also tracked other mass shootings. In one post, he appeared to urge readers to watch the online footage of Vester Flanagan shooting two former colleagues live on TV in August in Virginia, noting “the more people you kill, the more you’re in the limelight”.
He may have even posted a warning. A message on 4chan – a forum where racist and misogynistic comments are frequent – warned of an impending attack, but it is unclear if it came from Harper-Mercer.
“Some of you guys are alright. Don’t go to school tomorrow if you are in the northwest,” an anonymous poster wrote a day before the shootings.
On Thursday morning, he walked into Snyder Hall at the college and began firing, shooting many victims repeatedly.
Survivors described a classroom of carnage, and one said he ordered students to state their religion before shooting them.
Janet Willis told The Associated Press her granddaughter, Anastasia Boylan, was in the classroom.
Ms Willis, who visited her granddaughter in hospital, said she told her the shooter was asking students about their faith.
“If they said they were Christian, he shot them in the head,” she said her granddaughter told her.
She said her granddaughter also told her the shooter handed a student who was not shot a package and told him to deliver it to authorities.
Students in a classroom next door heard several shots, one right after the other, and their teacher told them to leave.
“We began to run,” student Hannah Miles said. “A lot of my classmates were going every which way.”
An aunt of an army veteran hit by several bullets said he tried to stop the gunman from entering the classroom.
Wanda Mintz said her 30-year-old nephew, Chris Mintz, a student at the college, fell to the floor and asked the shooter to stop. But, she said, he shot Mr Mintz again and went inside.
Several years ago, Harper-Mercer moved to Winchester, Oregon, from Torrance, California, with his mother, a nurse named Laurel Harper.
His father, Ian Mercer, originally from the United Kingdom, told reporters outside his Tarzana, California, home: “I’m just as shocked as anybody at what happened.”
At school in Oregon, “he was a typical Roseburg kid, kind of nerdy, kind of out there. Just himself,” said Alex Frier, a stage manager at the college who said Harper-Mercer built sets for theatre performances last term.
A neighbour, Bronte Harte, said Harper-Mercer “seemed really unfriendly” and would “sit by himself in the dark in the balcony with this little light”.
She said a woman she believed to be Harper-Mercer’s mother also lived upstairs and was “crying her eyes out” Thursday.
The army said Harper-Mercer failed basic training in 2008.
Army spokesman Lieutenant Colonel Ben Garrett said Harper-Mercer was in the military for a little over a month at Fort Jackson, South Carolina, but was discharged for failing to meet the minimum standards.
In Washington, President Barack Obama lamented the government’s inability to pass stricter gun laws even after attacks like the one in Oregon.
At a news conference at the White House, Mr Obama said he plans to keep talking about the issue and “will politicise it” because inaction is itself a political decision the US is making.
He said it is impossible to identify mentally ill people likely to perpetrate mass shootings ahead of time.
The only thing the US can do, he explained, is ensure they do not have an arsenal available “when something in them snaps”.