A law enforcement official says the Florida airport gunman told the FBI in November that the government was controlling his mind and was forcing him to watch Islamic State group videos.
The official was not authorized to discuss an ongoing investigation by name and spoke Friday on condition of anonymity.
The official says agents in Anchorage completed their interview with 26-year-old Esteban Santiago and called the police, who took him for a mental health evaluation.
The FBI's Anchorage field office said in a statement that it was aware Santiago was an Anchorage resident and that it was assisting in the investigation, but it declined to comment further.
Here's what we know about the suspect:
The suspected shooter has been identified as 26-year-old Esteban Santiago. Senator Bill Nelson said a TSA administrator and director of the airport told him that the shooter was carrying a military I.D. with that name. ABC News confirmed the suspect's name with law enforcement sources, but he has not been officially named as the suspect in the case.
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His supervisors at Signal 88 were apparently concerned about things he had expressed - so concerned that they brought him to the attention of the FBI office in Anchorage. It is unclear what assessment was made by the FBI, a second source confirms he did have contact with the FBI before the shooting.
Sources tell ABC News the alleged suspect received mental health treatment after the encounter with the FBI.
Santiago was born in New Jersey, but a state official said he apparently hasn't lived in New Jersey for "quite some time." His supervisors at Signal 88 was
He has a recent address listed in Anchorage, Alaska.
A military spokeswoman says the suspect in a deadly shooting at the Fort Lauderdale, Florida, airport received a general discharge from the Alaska Army National Guard last year for unsatisfactory performance.
Lt. Col. Candis Olmstead did not release details about Santiago's discharge in August 2016. Olmstead said that he joined the Guard in November 2014.
Puerto Rico National Guard spokesman Maj. Paul Dahlen said that Santiago was deployed to Iraq in 2010 and spent a year there with the 130th Engineer Battalion, the 1013th engineer company out of Aguadilla.
Olmstead also said that Santiago had served in the Army Reserves prior to joining the Alaska Army National Guard.
Santiago's brother, Bryan, told The Associated Press 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 over the telephone.
"We have not talked for the past three weeks," Bryan Santiago said. "That's a bit unusual ... I'm in shock. He was a serious person ... He was a normal person."
He said Esteban Santiago was born in New Jersey but moved to Puerto Rico when he was 2.
"Only thing I could tell you was when he came out of Iraq, he wasn't feeling too good," his uncle, Hernan Rivera, told The Record newspaper.
Maria Ruiz told The Record that her nephew had recently become a father and was struggling.
"It was like he lost his mind," she said in Spanish of his return from Iraq. "He said he saw things."
Santiago was flying from Anchorage on a Delta flight and had checked only one piece of luggage, which contained the gun.
Santiago was charged in a domestic violence case in January 2016, damaging a door when he forced his way into a bathroom at his girlfriend's Anchorage home. The woman told officers he yelled at her to leave, strangled her and smacked her on the side of the head, according to charging documents.
A month later municipal prosecutors said he violated the conditions of his release when officers found him at her home during a routine check. He told police he had lived there since he was released from custody the previous month. His Anchorage attorney, Max Holmquist, declined to discuss his client.
Law enforcement officers were at the girlfriend's home Friday afternoon, and officers guarding the property outside told a reporter who approached the home to step away.
The Pentagon said Santiago had gone AWOL several times during his stint with the Alaska National Guard and was demoted - from specialist to private first class - and given a general discharge, which is lower than an honorable discharge.
Rank: Private First Class (E3) effective February 2016
MOS/Branch: Combat Engineer (12B)
Component: Puerto Rico National Guard; Alaska National Guard
Dates of Service: December 2007 to August 2016
April 2008 to November 2008: Puerto Rico National Guard November 2008 to March 2009: Fort Leonard Wood, Missouri March 2009 to March 2010: Puerto Rico National Guard March 2010 to April 2011: Fort Dix, New Jersey April 2011 to February 2014: Puerto Rico National Guard February 2014 to November 2014: Inactive Ready Reserve November 2014 to August 2016: Alaska National Guard August 2016: transferred to Inactive Ready Reserve
Iraq (April 2010 to February 2011)
Army Commendation Medal
Army Good Conduct Medal
National Defense Service Medal
Iraq Campaign Medal with campaign star
Global War on Terrorism Service Medal
Armed Forces Reserve Medal w/ "M" Device Army Service Ribbon Overseas Service Ribbon Combat Action Badge Driver and Mechanic Badge - Wheeled Vehicle
The Fort Lauderdale mayor told reporters that the shooter was a "lone gunman" and didn't appear to be working with anyone else.
HOW HE ARRIVED AT FLL:
Law enforcement officials said Santiago boarded a plane Thursday night in Anchorage, Alaska, changed planes in Minneapolis and flew to Fort Lauderdale Friday.
Once he got off the plane, officials said he claimed his checked baggage, went into a restroom and came out shooting.
Officials said Santiago was arrested after he apparently ran out of ammunition at the airport. He was lying down at the terminal when he was taken into custody.
Authorities say five people were killed and eight wounded in the shooting.
The Associated Press contributed to this report.