A US army veteran who complained that the government was controlling his mind drew a gun from his checked luggage on arrival at the Fort Lauderdale airport and opened fire in the baggage claim area Friday, killing five people and wounding eight, authorities said.

He was taken into custody after throwing his empty weapon down and lying spread-eagle on the ground, one witness said.

The gunman was identified as 26-year-old Esteban Santiago of Anchorage, Alaska, who served in Iraq with the National Guard but was demoted and discharged last year for unsatisfactory performance. His brother said he had been receiving psychological treatment recently.

Mental health history

Santiago was deployed in 2010 as part of the Puerto Rico National Guard, spending a year with an engineering battalion, according to Guard Spokesman Maj. Paul Dahlen. He later joined the Alaska National Guard.

A law enforcement official told The Associated Press that Santiago had walked into the FBI office in Anchorage in November, 2016 to say that the US government was controlling his mind and making him watch Islamic State videos.

In November, 2016 Esteban told FBI agents in Alaska that the government was controlling his mind and was forcing him to watch Islamic State group videos, a law enforcement official said.

The official was not authorised to discuss an ongoing investigation by name and spoke Friday on condition of anonymity.

The FBI agents notified the police after the interview with Santiago, who took him in for a mental health evaluation.

Santiago's brother, Bryan, told the AP that his brother had been receiving psychological treatment in Alaska. He said Santiago's girlfriend alerted the family to the situation in recent months. Bryan Santiago said that he didn't know what his brother was being treated for and that they never talked about it.

“Only thing I could tell you was when he came out of Iraq, he wasn't feeling too good,” Santiago's uncle, Hernan Rivera, told The Record newspaper.

Since returning from Iraq, Santiago served in the Army Reserves and the Alaska National Guard in Anchorage. He was serving as a combat engineer in the Guard before his discharge for “unsatisfactory performance,” said Lt. Col. Candis Olmstead, a spokeswoman. His military rank upon discharge was E3, private 1st class, and he worked one weekend a month with an additional 15 days of training yearly, Olmstead said.

She would not elaborate on his discharge, but the Pentagon said Santiago had gone AWOL several times during his stint with the Alaska National Guard, adding he was demoted from specialist to private first class and given a general discharge, which is lower than an honorable discharge.

A work of 'terrorism' or 'mental health issue'?

Shortly after the shooting, and before details of Santiago's mental health became public, Sen. Bill Nelson of Florida said that it remained to be seen whether it was terrorism or the work of “someone who is mentally deranged.”

Piro said authorities are looking at leads in several states and have not ruled out terrorism. “We're looking at every angle, including the terrorism angle,” he said.

Santiago, who is in federal custody, will face federal charges and is expected to appear in court Monday, Piro said.