The gunman who killed nine people and wounded seven others in Oregon had targeted Christians, the father of one of the victims says.
Named as Chris Harper Mercer, the gunman opened fire on Thursday inside a classroom at Umpqua Community College.
Thirteen weapons were recovered, six at the school and seven at his home, the police said. All were bought legally.
Mercer had body armour, three pistols and a rifle when he was shot and killed by police officers after a gun battle.
On Friday, US President Obama repeated his calls for Congress to toughen up the gun laws.
And he urged the public to apply pressure to their local politicians.
"You have to make sure that anybody who you are voting for is on the right side of this issue."
Earlier, Stacy Boylan, whose daughter survived the shooting, told US television network CNN that his daughter described to him how the gunman asked his victims to state their religion before shooting them.
"'Are you a Christian?' he would ask them, 'and if you are a Christian stand up,'" the father recalled.
Mr Boylan said the gunman told the victims: "because you're a Christian you're going to see God in just about one second".
Another student who survived the shooting, Kortney Moore, gave a similar account to a local newspaper, The News-Review.
It also emerged that he enlisted in the Army in 2008, but he was discharged after less than a month in basic training, for unknown reasons.
The attacker was identified by unnamed officers, as local police refused to release his name.
Douglas County Sheriff John Hanlin said he did not wish to give the gunman "the credit he probably sought prior to this horrific and cowardly act".
However, the sheriff has come under fire for his stance opposing gun control measures in the past.
At the scene: Vanessa Barford, BBC News, Roseburg, Oregon
Twenty-four hours after a 26-year-old gunman went on a ruthless shooting spree, the college is cordoned off by police tape, a "pray for Rosebury" sign up against the fence.
Just 200 metres up the road at Del Ray Cafe, local residents are heartbroken by the tragedy.
"This is a close knit community. Everyone knows everyone. We have a group of professors from the college for breakfast every Friday. They were in shock this morning. Everyone is devastated," the manager said.
Customer Victor Moffett, 82, wired the electrics in the science building - where some of the victims lost their lives - 30 years ago.
"It's terrible. A neighbour called me yesterday saying her friend's daughter had been shot in the leg. She was really upset. I never thought I'd see something like that where I live," he said.
Another local couple in their 60s, who wished to remain anonymous, were visibly angry.
"[The gunman] thought he could make a splash - and he did. Now Obama is using it to jump start gun crime. That doesn't work here. It's too bad they couldn't get him as soon as he fired the first shot," the man said.
Hours after the attack, President Obama reiterated demands for tighter gun laws, saying prayers are "no longer enough".
Candidates vying to replace Mr Obama in office have begun to weigh in as well.
The gunman was reportedly born in the UK and moved to the US as a young boy.
A man identified as the gunman's father, Ian Mercer, told US media he was "just as shocked as everybody" by his son's actions.
The killer's motive is not known, although police said they were investigating reports that he had warned of his intentions on social media.
Oregon college shooting - in depth
Army vet 'hero' in Oregon shooting - the man that tried to stop the attack
US gun violence in numbers - Shootings have become increasingly commonplace.
What we know about Chris Harper Mercer - The alleged gunman reportedly supported the IRA.
Oregon shooting: The '4chan' thread - Did the gunman give a warning on the Internet?
Suspect's father speaks out - Ian Mercer says he is shocked and appealed for privacy.
In an online profile appearing to belong to the gunman, he listed hobbies including the internet and "killing zombies", described his politics as "conservative, republican" and said he was spiritual but not religious.
Lorie Andrews, who lives opposite the campus, said she heard what sounded like fireworks and when she came out of her home she saw students streaming out.
"One girl came out wrapped in a blanket with blood on her," she said.
Hannah Miles, 19, said that she and fellow students were led to a nearby bookshop, where they hid in a back room.
Hundreds attended a vigil to remember the victims on Thursday evening.