Who is Esteban Santiago, the man accused of mass murder at Fort Lauderdale airport?

The FBI are currently interviewing a suspected gunman believed to have killed five people and injuring eight others at Fort Lauderdale airport in the latest mass shooting to shock the US.

The assailant opened fire Friday afternoon at Fort Lauderdale-Hollywood International Airport, reportedly firing until he ran out of ammunition. He then handed himself into police, without resisting.

As the victim's families pick up the pieces after the latest mass shooting on the US, Esteban Santiago, a 26-year-old security guard from Anchorage, Alaska, remains the FBI's only suspect. He faces the death penalty in Florida, if he's convicted.

Authorities will now assess exactly how and why the killings took place with charges expected to be brought imminently.

Authorities believe Santiago flew to Florida from Anchorage via Minneapolis on Delta airlines then went to baggage claim and picked up his one piece of checked luggage, which contained a handgun, on arrival.

In the US taking a gun on a plane is legal, if it is unloaded, the weapon is in a case that locks and it is checked into a bag.

Santiago, who was believed to have been wearing a blue Star Wars T-shirt, is alleged to have gone to the bathroom to load the handgun and began shooting innocent civilians when he emerged.

At the moment two people, Terry Andres, of Virginia, and Olga Woltering, of Georgia, have been named as fatalities.

Reports of a possible altercation involving Santiago on the flight to Florida have not been confirmed by the airline or law enforcement officials. The FBI has not ruled out terrorism as a motive.

Santiago has been identified by multiple law enforcement officials as the lone gunman and he is currently being held without bond on a murder charge.

The suspect is a former US Army soldier from Puerto Rico. His brother, Bryan Santiago, told NBC News he served in the National Guard on the island. He was then deployed to Iraq for 10 months where he was awarded a combat action badge, and served in total, for nine years.

His aunt, Maria Ruiz, told NorthJersey.com that Santiago had a girlfriend and a newborn child, but after returning from Iraq began acting strangely, but seemed happy after the birth of his child in September.

Santiago is then believed to have moved to the US Army Reserves and later moved to Alaska, where he served as a combat engineer in the Alaska National Guard. He served in Alaska from November 2014 until August when he was discharged for unsatisfactory performance in August last year, a spokeswoman for the National Guard said.

Federal law enforcement officials have stated that Santiago was undergoing treatment for mental health problems after he complained that he was hearing voices.

It has been reported that in November last year Santiago had a mental evaluation after he visited the FBI's regional office in Anchorage saying that his mind was being controlled by a US intelligence agency and that it was forcing him to join Islamic State (Isis), reported CNN.

Indeed in some pictures emerging online Santiago is seen using a pose holding up one finger, which is popular with IS (Daesh) militants who claim it represents the "oneness of god" and that events on Earth are all god's will.

A senior federal law enforcement official said that during the interview he appeared agitated and incoherent throughout the interview. US media reported that Santiago is undergoing psychiatric evaluation.