(CNN) The father of the Roseburg, Oregon, shooter said he doesn't know where his son got his weapons, and he declined to comment much on his son's mental state, but he was quick to say what he thought was to blame in the deadly college attack: Guns.

Ian Mercer, during an interview outside his California home Saturday, told CNN that he didn't know his son had a single gun, let alone 13. He asked, "How on earth could he compile 13 guns? How could that happen?"

A patient is wheeled into the emergency room at Mercy Medical Center in Roseburg on October 1.

A patient is wheeled into the emergency room at Mercy Medical Center in Roseburg on October 1.

People gather at a roadblock near the entrance to the college on October 1.

People gather at a roadblock near the entrance to the college on October 1.

A bullet casing is marked at the scene of the shooting on October 1.

A bullet casing is marked at the scene of the shooting on October 1.

A woman is comforted after the deadly shooting at Umpqua Community College in Roseburg, Oregon, on October 1. Douglas County Sheriff John Hanlin announced at a news conference that the shooter was dead.

A woman is comforted after the deadly shooting at Umpqua Community College in Roseburg, Oregon, on October 1. Douglas County Sheriff John Hanlin announced at a news conference that the shooter was dead.

Students and faculty are reunited with friends and family at the county fairgrounds on October 1.

Students and faculty are reunited with friends and family at the county fairgrounds on October 1.

In response to the shooting on October 1, President Barack Obama delivers the 15th statement of his presidency addressing gun violence. "Somehow this has become routine," he said. "The reporting is routine. My response here at this podium ends up being routine, the conversation in the aftermath of it. We've become numb to this."

In response to the shooting on October 1, President Barack Obama delivers the 15th statement of his presidency addressing gun violence. "Somehow this has become routine," he said. "The reporting is routine. My response here at this podium ends up being routine, the conversation in the aftermath of it. We've become numb to this."

Community members attend a candlelight vigil at Stewart Park for those killed during a shooting at Umpqua Community College in Roseburg, Oregon, on Thursday, October 1. The massacre left nine people dead and nine wounded. The gunman also died.

Community members attend a candlelight vigil at Stewart Park for those killed during a shooting at Umpqua Community College in Roseburg, Oregon, on Thursday, October 1. The massacre left nine people dead and nine wounded. The gunman also died.

Mercer's son, Chris Harper-Mercer, staged an attack at Umpqua Community College, killing nine people and injuring nine others Thursday.

During his interview, Ian Mercer appeared to walk back his statement that guns were to blame, but only briefly.

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"We talk about gun laws. We talk about gun control. Every time something like this happens, they talk about it and nothing gets done. I'm not trying to say that that's to blame for what happened, but if Chris had not been able to get hold of 13 guns, this wouldn't have happened," the father said.

Mercer said he has never held a gun. He doesn't want to, he said. He laid out his personal philosophy on the issue: "I'm a great believer (in) you don't buy guns, don't buy guns, you don't buy guns."

Other countries don't see mass shootings at the same clip that the United States does, he said, asserting, "Somebody has to ask the question: How is it so easy to get all these guns?"

His condemnation of guns grew stronger as the interview went on, and he closed his remarks on the subject with a call for change.

"It has to change. How can it not? Even people that believe in the right to bear arms, what right do you have to take people's lives? That's what guns are, the killers. Simple as that. Simple as that. It's black and white. What do you want a gun for?"

Pressed on whether his son's mental state could be to blame for the violence, Mercer declined to comment, saying he wanted to let police follow through, but he left open the possibility that his son's state of mind could have played a role.

"Obviously, somebody who goes and kills nine people has to have some kind of issue. Whatever it is, let the police determine what they find," he said.