May 24, 2017 0354 GMT
Esteban Santiago, a 26 year-old resident of Anchorage, Alaska, was taken into custody immediately following the shooting and questioned at length, according to officials at the Federal Bureau of Investigation (FBI).
Federal investigators had not ruled out terrorism as a possible motive in the massacre and were examining the suspect's recent travels, said George Piro, special agent in charge of the FBI office in Miami, Florida.
Santiago retrieved a semi-automatic handgun from his checked luggage and began firing indiscriminately after arriving in Fort Lauderdale–Hollywood International Airport from Alaska.
One witness said the attacker kept shooting until he ran out of ammunition for his handgun.
The airport remains closed and planes scheduled to land there have been diverted to other airports in Florida.
"This is a senseless act of evil," Florida Governor Rick Scott told reporters.
A White House spokesman said President Barack Obama had spoken to Scott and other state officials. Obama said such tragedies had happened too often during his eight-year-term in office.
Incoming President Donald Trump said that it is a "disgraceful situation that's happening in our country and throughout the world" and that it was too soon to say whether it was a terrorist attack.
Santiago was sent to Iraq in 2010 and spent a year there as a combat engineer while serving the Puerto Rico National Guard. He later joined the Alaska National Guard.
His family members said he had been receiving treatment for mental problems which began after he returned from Iraq.
Maria Luisa Ruiz, Santiago’s aunt from Union City, New Jersey, said, "He lost his mind. He said he saw things."
A federal law enforcement official said Santiago had entered into an FBI office in Anchorage in November and was behaving erratically and was turned over to local police, who took him to a mental facility for evaluation.
During that visit, he told FBI agents that his mind was being controlled by a US intelligence agency, which was ordering him to watch videos by the Daesh (ISIL) terrorist group.