The slain security worker was the first TSA officer killed in the line of duty in the 12-year history of the agency, which was founded in the aftermath of 9/11.
The FBI and Los Angeles Airport Police identified the gunman as Paul Ciancia, 23, of Pennsville, N.J. He had apparently been living in Los Angeles.
A law enforcement official, speaking on condition of anonymity because the person was not authorized to discuss the investigation publicly, said Ciancia was wearing fatigues and carrying a bag containing a one-page handwritten note that said he wanted to kill TSA employees and "pigs."
The official said the rant refers to how Ciancia believed his constitutional rights were being violated by TSA searches and that he's a "pissed-off patriot" upset at former Department of Homeland Security Secretary Janet Napolitano. The note and the gunman's rifle each had an orange TSA inspection sticker on it.
Ciancia had at least five full 30-round magazines on him, said the official, who was briefed at LAX on the investigation. The official said Ciancia was shot in the mouth and leg by two airport police officers. Another official briefed on the incident at LAX who could not speak publicly said the gunman had been shot four times but was "stable" when he was transported to the hospital.
Early Friday afternoon, Ciancia's father in New Jersey had called authorities for help in finding his son after the young man sent one of his siblings a text message about committing suicide, Pennsville Police Chief Allen Cummings said.
The chief said he called Los Angeles police, which sent a patrol car to Ciancia's apartment. There, two roommates said that they had seen him Thursday and that he was fine, according to Cummings.
Cummings said that the Ciancias — owners of an auto body shop — are a "good family" and that his department had had no dealings with the son.
The attack began around 9:20 a.m. when the gunman pulled an assault-style rifle from a bag and began firing inside Terminal 3, Airport Police Chief Patrick Gannon said. The terminal serves such airlines as Virgin America, AirTran, Spirit Airlines, Horizon Air and JetBlue.
The gunman then went to the security screening area, where he fired more shots and went into the secure area of the terminal, Gannon said. Officers exchanged fire with him and seized him, Gannon said.
As gunfire rang out, panicked travelers dropped to the ground. Those who had made it past security ran out of the terminal and onto the tarmac or took cover inside restaurants and lounges.
"We just hit the deck. Everybody in the line hit the floor and shots just continued," said Xavier Savant, who was waiting in the security line where the shooting took place. He described it as a "Bam! Bam! Bam!" burst of gunfire.
Savant said people bolted through the metal detectors and ran into the terminal.
"My whole thing was to get away from him," said Savant, an advertising creative director who was heading to New York with his family for a weekend trip.