The father of the man who attacked a gay nightclub in Orlando, Fla., said Monday he would have turned his son over to authorities if he had known his plans.
"I would have arrested him myself. I would have called the FBI, I would have called local law enforcement," Seddique Mir Mateen said of Omar Mateen, who died in a gun battle with police inside the club early Sunday.
"I don't know why he did what he did. I wasn't aware of it," Mateen told reporters, apologizing again for his son's actions in the deadliest mass shooting in U.S. history.
Omar Mateen gunned down 49 people and left dozens more injured before he was killed in a shootout with police. Authorities are investigating any international terrorist ties to the attack, which officials are calling an act of domestic terrorism.
Mateen told reporters that he wouldn't allow anyone to commit a terrorist act in the United States.
"My principle as a father, my principle as a U.S. citizen, I'm against — I've been, throughout my life — against terrorism, against injustice, against what anyone can do against the United States," he said. 
"It is very sad news today for all Americans, and I am very, very mad," he said.
Mateen said Sunday that his family is shocked and he doesn't believe his son's motive had anything to do with religion. News reports said Omar Mateen claimed allegiance to the leader of the Islamic State in Iraq and Syria during his assault.
Seddique Mir Mateen told NBC News his son grew "very angry" when he saw two men kissing in front of his wife and child earlier this year in Miami and speculated it might have in part motivated the attack on the gay nightclub.