The heroic father who shot the gunman who killed three children and a teacher inside an Oregon elementary school happened to drive by the building when he heard shots fired.

Kaylub Giamanco, 36, was driving past his daughters' school on his way home for lunch on Thursday when he heard gunfire. 

He is a carpenter and a father of two girls, ages 5 and 10, who attend Silver Rail Elementary, his brother told NBC News.

After hearing the gunshots, he followed 16-year-old shooter Griffin John II, who previously attended the school, into the building, his brother, Kyle, said.

Kyle explained that his brother owns a concealed weapon and followed the shooter into the special education room.

John II killed three students ages 5, 8 and 11, and a teacher, before he was shot by Giamanco, authorities said. Another teacher and a seven-year-old student were injured.

Giamanco doesn't feel like a hero because he is haunted by what he saw in the classroom and feels guilty that he didn't save more people, his brother said.

The Giamanco family is friends with the family of the seven-year-old who was injured. The seven-year-old is a wheelchair user and was shot in the face.

Kyle said the child is recovering from surgery.

President Donald Trump praised Giamanco for stopping the Oregon school shooting.

'Well, I'll tell you what, there was a great hero. It could have been worse, as bad as it was. We had a great hero that went in and did the business,' Trump told reporters outside of the White House on Friday.

'He took care of business, and thank God we had him. Otherwise, it would have been much worse. It's a terrible thing, but thank goodness for a man that had a gun and knew how to use it.'

During a press conference on Thursday, Oregon Governor Tina Kotek called Giamanco a hero.

'To the community member who heroically intervened to stop further loss of life: Your actions carry a heavy emotional burden, and I just want you to know that my thoughts are with you as well,' Kotek said.

A GoFundMe has been set up for Giamanco to help pay for therapy, any legal expenses he may face and to support him while he takes time off work following the tragedy.

'Kaylub, his wife Kelsey and their two young daughters have an incredibly difficult road ahead of them,' the fundraiser stated.

'The emotional and psychological impact of this tragedy cannot be overstated, and they deserve the time, space and resources to begin healing together.'