The gunman, who was 26, opened fire at Umpqua Community College on Thursday morning.
Anastasia Boylan, 18, was in the room when the assailant, thought to be called Chris Harper Mercer, came into her classroom at Umpqua Community College in Roseburg and shot her teacher at point-blank range, immediately killing him.
Ms Boyland told her family Chris Harper Mercer then began asking people in the room whether they were Christians or not, before forcing them to stand up if they were.
He then shot them, Ms Boyland said.
Mr Mercer also shot Ms Boylan, who only survived by playing dead.
Her father, Stacy Boylan, told CNN while his daughter was receiving surgery on her spine: "[Harper Mercer] came in and there was gunfire immediately and he scattered the room. From what I understood what she said was he shot the professor point blank, one shot killed him.
"Others had been injured and then this man had enough time - I don't know how much time elapsed - he was able to stand there and start asking people one by one what their religion was.
"'Are you a Christian?' he would ask them, and 'if you are a Christian then stand up' and they would stand up. He'd say 'because you are a Christian you're going to see God in about one second' and then he shot and killed them. And he kept going down the line doing this to people.
"How much time do you need?
"She said he had a handgun. It wasn't a big rifle or an assault rifle. This was a single handgun and he had enough ammunition and enough time to drop the magazine out of it, put another one in and continue his thing.
"How does he have that much time at a facility? I don't understand that. How he could have that much time to kill that many people?"
Hours after the attack, where seven were injured, a frustrated President Barack Obama demanded tighter gun laws, saying prayers are "no longer enough".
CBS Los Angeles reported that Mercer's stepsister had told the station he was born in the United Kingdom and travelled to the United States as a young boy.
The gunman was also killed in a police shootout.
On the internet his blog documents an interest in mass shootings including a recent post about the gunman who killed two US journalists live on air in August.
He describes killer Vester Flanagan as a man who "wanted the world to see his actions". Before adding: "Seems the more people you kill, the more you're in the limelight"
Another blog post discussing the recent shooting of a Houston police officer said he did not "agree with the black lives matter protests".
A screenshot taken from Chris Harper-Mercer's MySpace page.
President Obama said that: "We are the only advanced country on earth that sees these kinds of mass shootings every few months."
Listen to President Barack Obama's speech in response to the Umpqua Community College shooting:
Listen to Premier's Hannah Tooley speak to American Pastor Kurt Erikson's from Elios Ministries. He works in the UK:
