Was it PTSD?

The Army veteran who killed five people and wounded eight others at the Fort Lauderdale-Hollywood International Airport Friday afternoon had been receiving psychological treatment, according to family members.

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The shooter is in police custody and investigations are underway.

Twenty-six-year Esteban Santiago lived in Anchorage, Alaska, and had been receiving psychological treatment there, according to his brother, Bryan Santiago, The Associated Press reported. Santiago’s girlfriend had alerted the family to the situation in recent months, though the brother did not know what Santiago was being treated for exactly.

Santiago flew Friday from his home in Anchorage to Fort Lauderdale with a gun checked in his luggage. The gun was the only thing he had in his luggage, police said.

Witnesses said he picked up his bag, went to the restroom, loaded his gun, then returned to the baggage claim area. He then opened fire without saying a word, shot until he ran out of bullets, then lay on the floor waiting for police to nab him, witnesses said — although one also said the shooter reloaded the gun at one point.

Related: Shootings at Fort Lauderdale Airport

It is legal for airline passengers to travel with guns and ammunition as long as the firearms are in a checked bag — not a carry-on — and are unloaded and locked in a hard-sided container. Guns must be declared to the airline at check-in.

Santiago had served in Iraq with the National Guard, but last year was demoted and discharged for unsatisfactory performance, the AP reported. An aunt, Maria Ruiz, told NJ.com Santiago “lost his mind” after his overseas service. He was hospitalized for mental health issues when he initially returned, according to The (New York) Daily News.

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He then moved to Alaska where he joined the National Guard, but was discharged there as well after going AWOL several times. In November, he reportedly walked into an FBI office and said he was being forced to fight for ISIS.

The Military Times shared more details about his earlier service: Santiago was deployed to Iraq in 2010 and spent a year there with the 130th Engineer Battalion’s 1013th Engineer Company out of Aguadilla, according to Puerto Rico National Guard spokesman Maj. Paul Dahlen.

Related: How Veterans Can Fight Their Way Through PTSD

Santiago was a private first class who served as a combat engineer in the Puerto Rico National Guard and Alaska National Guard, according to service records released Friday evening by the Army. He served from Dec. 2007 to August 2016, deploying to Iraq from April 2010 to February 2011, according to Army records. During his service, Santiago earned awards typical of someone of his rank, time in service and experience. They include the Army Commendation Medal, Iraq Campaign Medal with campaign star, and Combat Action Badge.

Ruiz, the aunt, said Santiago had been working a security job in Alaska, became a father last year, and “seemed fine” over the holidays.