A suspect is in custody in Florida after a man opened fire at Fort Lauderdale airport, killing five people and wounding eight others.
The suspect is believed to be 26-year-old Esteban Santiago, an Iraq war veteran.
The motive is under investigation, but officials said he probably acted alone.
US media said the man might have been mentally disturbed. He reportedly said the government was controlling his mind and made him watch jihadist videos.
The suspect was in possession of a military ID which suggested he was a former member of the Puerto Rico and Alaska National Guard. He served in Iraq from April 2010 to February 2011, and ended his service in August 2016, according to the Pentagon.
His brother said he had been receiving psychological treatment recently.
He surrendered to police when he ran out of ammunition, witnesses added.
The attacker opened fire at the baggage claim area of Terminal 2 as passengers were collecting their luggage.
The man, who was wearing a Star Wars T-shirt, had travelled from Alaska and checked in an unloaded gun and ammunition with his luggage. He loaded the weapon in the bathroom after landing and collecting his bag.
Flying with firearms is legal in the US as long as the guns are kept in a locked, hard-sided container as checked baggage only, under rules of the Transport Security Administration (TSA). Ammunition is allowed only in checked luggage.