Iraq war vet Esteban Santiago flew to the Fort Lauderdale airport on Friday and retrieved a 9mm semi-automatic handgun and ammunition that he had declared and packed in his checked luggage.
Video released by the TMZ website showed Santiago, bearded and wearing a blue shirt, walking calmly through the baggage claim area.
He strolled past some passengers before nonchalantly removing a gun from his waistband and shooting it, then running off the screen.
One woman hid behind a luggage cart as others ducked for cover following a brief moment of stunned confusion.
TMZ did not say where it obtained the video, and showed only a 20-second portion that included the moments leading up to the attack and the first shots.
According to authorities, Santiago, who had previously shown signs of "erratic behavior," continued shooting until he ran out of ammunition.
He then put down the gun, dropped to the ground and was quickly detained by sheriff's deputies, FBI agent Michael Ferlazzo said in court documents.
The suspect, who traveled from Alaska on a one-way ticket and told investigators he had planned the attack, fired approximately 10 to 15 rounds, shooting methodically while "aiming at his victims' heads," Ferlazzo said.
The US Justice Department on Saturday charged Santiago, 26, with firearms offenses and carrying out an act of violence at an airport, for which he could face the death penalty or life in prison if convicted.
He is scheduled to make an initial court appearance on Monday.
FBI special agent George Piro said agents were looking into motives for the attack, including "continuing to look at the terrorism angle."
- Mental health history -
A former member of the Puerto Rico and Alaska National Guard, Santiago served in Iraq from April 2010 to February 2011. He ended his service in August.
On November 7, he walked into the FBI's office in Anchorage, Alaska and complained that his mind was being controlled by national intelligence agencies, which were forcing him to watch Islamic State jihadist videos, the authorities said.
This "erratic behavior" led agents to contact local police, who took him for a mental health evaluation, Piro said.
According to several testimonies, including from his brother and an aunt, Santiago was suffering from mental health problems.
Broward County Sheriff Scott Israel told CNN Sunday that two of the wounded victims remained in intensive care while the other four had been released or were recovering in the hospital.
Authorities have not identified any of the victims, but three named in media reports were all getting ready to set off on cruises.
"One of the ladies that was killed was my seatmate on the plane and she was standing right next to me in the baggage claim," one visibly distressed witness told local broadcaster WSVN.
"The pops started. I hit the ground and I turned around and she was shot in the head and killed," she said choking back tears.
The victims included British-born 84-year-old grandmother Olga Woltering, who was embarking on a family cruise with her 90-year-old husband, the Sun Sentinel reported.
Terry Andres, 62, was going on vacation with his wife of nearly four decades, Ann, the Palm Beach Post reported.
Other victims included Michael and Kari Oehme, a couple in their 50s. Michael was killed and his wife wounded in the shoulder, the Miami Herald reported.