Esteban Ruiz Santiago is accused of murdering five people at the Fort Lauderdale-Hollywood International airport on Friday.
During a 15-minute court appearance on Monday he was told by the judge that he may face the death penalty.
Santiago answered the judge's questions in a clear voice.
He spoke very little during the hearing and confirmed to the judge that he understood the criminal charges and that he is a US citizen.
When asked about his employment, he told the judge that he worked for the Signal 88 security firm in Anchorage, Alaska, for the last few years and that he currently has only $5 to $10 in his bank account.
Security was high outside the courtroom, with more than 25 armed police guarding the building.
Santiago wore a red jumpsuit and was shackled at the wrists, stomach and legs throughout the hearing.
Authorities say they have not ruled out terrorism as a motive, and that they are investigating whether mental illness may have played a role in the attack.
In November 2016, Santiago visited an FBI building in Anchorage to tell agents he was hearing voices and believed that US spies were trying to control his mind.
According to a criminal complaint, Santiago told investigators that he flew one-way from Alaska to Florida to carry out the attack.
Agents say he checked a handgun into his luggage.
He retrieved the gun from the baggage carousel, and loaded it in a bathroom before emerging and firing at random, investigators say.
Six other people were wounded by gunshots at the airport's baggage claim area.
Three dozen suffered minor injuries in the chaos as passengers and airport workers fled.

The school's headmaster said the "growing expense and luxury" forced on parents was also a major concern.
Beaulieu Convent School in Jersey also referred to "worries about alcohol and drug consumption" at the end of Year 11 event for pupils aged 15-16.
A former pupil said the prom was an important milestone and accused the school of overreacting.
Chris Beirne, headmaster, said the "significant focus and distraction" caused by the prom "does not fit into the ethos of our school".
Writing to parents Mr Beirne cited a letter from an unnamed colleague who was convinced the preparations and the event were "not positive, constructive or healthy experiences".
The colleague wrote: "The financial strain and the inevitable competition associated with this is another very unwelcome, and sometimes crushing, aspect for many parents."
The letter from the colleague also referred to "alcohol and drug consumption at after-parties" as "a considerable concern".
It said the strain of trying "to be slim, fashionable, have perfect skin" led to "unacceptable pressure".
Mr Beirne said he could no longer "safely manage the risk" associated with the event.
The independent Catholic school said it would continue to offer Year 13 leavers a celebratory mass with their families followed by a drinks reception at the school.
The Â£5,400-a-year convent has around 760 students aged 4-18.
Former pupil Hannah Hosegood, 20, said her prom was "a first taste of maturity" and the school should tackle individual pupils if they had concerns about drugs or alcohol.
She said: "It's really upsetting knowing those girls won't be able to experience an event you spend a fair amount of time looking forward to and remember for the rest of your life."
A 26-year-old Iraq war veteran suspected of opening fire in a crowded Florida airport last week has appeared in court to hear charges against him.
[NEXT_CONCEPT]
A girls' school has scrapped its end of year prom claiming it is too much of a "distraction" to pupils.