The suspected shooter in Friday's deadly rampage at a Fort Lauderdale airport was charged on Saturday with federal counts that could carry the death penalty.
Esteban Santiago, 26, is accused of opening fire at Fort Lauderdale airport, killing five people and injuring six others.
He is charged with carrying out an act of violence at an international airport resulting in death, which carries a maximum punishment of execution.
Mr Santiago also faces lesser weapons charges.
The suspect, who is in custody, told agents he had planned the attack and bought a one-way ticket to Fort Lauderdale, according to court papers.
Authorities said they did not know why he chose this target and that terrorism had not been ruled out.
"Today's charges represent the gravity of the situation and reflect the commitment of federal, state and local law enforcement personnel to continually protect the community and prosecute those who target our residents and visitors," US Attorney Wifredo Ferrer said.
Mr Santiago is said to have used a semi-automatic handgun that he apparently legally checked on a flight from Alaska.
Officials were also looking whether mental health problems played a role after it emerged that the suspect had been referred for a health assessment by the FBI.
Last November, Mr Santiago walked into an FBI office in Alaska in an agitated and incoherent state, the FBI and Anchorage police said.
He was carrying a loaded magazine but had left his handgun in his car, with his newborn child.
During the later mental health evaluation, he told the FBI he was hearing voices and believed he was being controlled by a US intelligence agency.
His gun was confiscated but the authorities found no wrongdoing, and it was returned in December. It is not clear if this is the same gun that he is accused of using in the attack at the airport baggage claim area.
The charges against Santiago also carry the possibility of life in prison, the U.S. Attorney's Office said. He is expected to appear in a Fort Lauderdale federal court Monday morning.