Orlando nightclub shooter's father attends Hillary Clinton rally

KISSIMMEE, Fla. -- Hillary Clinton spoke Monday at a rally in Kissimmee, Fla.

Seddique Mateen, father of Orlando nightclub shooter Omar Mateen, was in the crowd behind the Democratic presidential nominee.

Clinton paid tribute to the victims of the deadly shooting, their grieving families and the first responders who rushed into the club to save as many people as they could.

As Clinton spoke, Seddique Mateen was seen sitting behind her, wearing a red hat.

Mateen did not say much to reporters at the event. But he did say he and his family have been cooperating with the federal investigation of the shooting.

About an hour later, WPTV ran into Mateen at a rest stop on the way back to West Palm Beach, Fla.

He said he thinks Hillary Clinton would be better for the country than her opponent, Donald Trump, and wanted to show his support. Mateen said he received an email from the Democratic Party about the rally and decided to attend.

When asked about his son in relation to the nightclub shooting, Mateen told WPTV he regrets Omar's actions.

"I wish, because I spoke a lot about that - I wish that my son joined the Army and fought ISIS and destroyed ISIS. That would be much better," Seddique Mateen said.

A Clinton campaign official told ABC News the rally was an open-door event with about 3,000 people in attendance. Seddique Mateen was not an invited guest and staffers did not know he was there until after the rally was over, the official said.