LOS ANGELES (CNN) -- It's not clear why a 23-year-old man, identified by the FBI as Paul Anthony Ciancia, stormed one of America's busiest airports, but it is clear he was dangerous.
And investigators were digging into his background to find out clues about his motives.
He had enough ammunition to "have literally killed everyone in that terminal," Los Angeles Mayor Eric Garcetti said.
Whatever the reason, the suspect, armed with what police say was an assault rifle, opened fire in Los Angeles International Airport's Terminal 3, killing one and sending dozens scattering before he was wounded and captured.
One clue to the suspect's intentions came from witnesses of the mayhem.
Some said the gunmen asked people, "Hey, are you TSA?" -- the acronym for the Transportation Security Administration. If they said "no," he would move on.
One of those questioned travelers was Leon Saryan. He told CNN's Anderson Cooper that the same man he'd just seen shoot a TSA officer "calmly" walked toward him and asked, "TSA?"
PHOTOS: Shooting at LAX (http://bit.ly/16sBuvr)
"I just shook my head," Saryan said. "And he kept going."
The materials found on the suspect included a rant that appeared to reference the New World Order as well as anti-TSA and anti-government claims, a federal law enforcement official said Saturday.
It's not clear what gave rise to the references, and federal investigators have found no known links to known groups or anything in the suspect's background to explain them. The New World Order is generally considered to be a conspiracy theory in which people suspect a group of elites are conspiring to form an authoritarian, one-world government.
The incident disrupted flights and inconvenienced passengers. As of Saturday morning, Terminal 3 remained closed, and it was unclear when it would reopen.
In a message on Twitter on Saturday morning, the airport said that from the start of the incident around 9:30 am Friday through midnight, an estimated 1,550 scheduled flights with about 167,050 passengers were "impacted."
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An officer killed
The TSA officer killed was the first employee of that relatively new agency to be killed in the line of duty. The agency identified him as Gerardo Hernandez, who would have turned 40 next week. He was working as a travel document checker at the time of the shooting, according to TSA workers' union and federal sources.
Two other TSA officers were also shot, one in the leg, authorities said.
The suspected gunman was detained after being shot in the chest multiple times, according to an intelligence source briefed by Los Angeles police. As of Friday evening, he was receiving medical attention at a hospital, according to FBI Special Agent in Charge David Bowdich.
Ronald Reagan UCLA Medical Center said that it received three male victims -- one in critical condition and two in fair condition. One of the two in fair condition suffered gunshot wounds, while another had an unspecified injury, said Dr. Lynne McCullough, an emergency physician at the Los Angeles hospital. One of them was released by Friday afternoon; one of the others who remained at the hospital was Ciancia, according to the intelligence source.
Two other patients were transported to Harbor-UCLA Medical Center in Torrance, said David Klurad, a trauma surgeon there.
Klurad described one as a "middle-aged" person with minor injuries from being shot in the shoulder. The other had no signs of life when he arrived at the hospital, the surgeon added.
Another clue to Ciancia's state of mind came from his family. He lives in Los Angeles, but his family back in New Jersey were concerned about him, said Allen Cummings, chief of police in Pennsville, New Jersey.
Ciancia's family became concerned in recent days after he sent his brother and father "angry, rambling" texts venting about the government, living in Los Angeles and his unhappiness generally, an intelligence source said.
But despite the unsettling text, Ciancia's family was still surprised by Friday's events.
"They're upset," Cummings told reporters. "I mean this is a shock to them, it's a shock to our community."
Terror in the terminal
The shooting caused what airport police Chief Patrick Gannon described as a "large amount of chaos."
People ran for their lives and took shelter wherever they could as authorities pursued the gunman.
Chuck Ocheret was among those in the busy airport when he heard two "loud pops."
"Then I heard this mad rush of people, and there was a stampede of people coming from this direction," Ocheret said. "Nobody really knew what was going on."
An otherwise normal day in the airport's Terminal 3 turned upside down around 9:20 a.m. (12:20 p.m. ET), as the suspect approached a checkpoint.
There, he "pulled an assault rifle out of a bag and began to open fire," Gannon said.
Passenger Saryan had just cleared the TSA checkpoint and was reaching for his shoes and belt when shots
rang out, prompting "everybody (to) hit the ground and ... run." A TSA officer grabbed Saryan's shoes and started running alongside him, before the gunman grazed the officer with a bullet.
"I went and cowered in a corner," Saryan said.
The suspect kept moving down Terminal 3, equipped with three magazines for his weapon, according to the intelligence source briefed by Los Angeles police. He began running down Terminal 3.
He had company. Gannon said two officers from his department responded "within seconds after the shooting started" and ran off in pursuit of the suspect.
Traveler Vernon Cardenas was sitting at one end of the terminal, when he heard noise and saw a mass of people running toward him. He and others bolted through a kicked-open exit door and ran onto the tarmac -- believing it was safer there.
The circular area where Cardenas had been is where the bloodshed finally ended with the gunman's shooting by law enforcement, according to the intelligence source. They didn't take any chances with the wounded suspect either, handcuffing him to a gurney as he was being carried out. Authorities said they found more than 100 rounds of unspent ammunition.
The gunfire was so unexpected and sudden that many panicked passengers ran out of the terminal to safety, leaving their belongings behind.
LAX officials tweeted that passengers would be able to return some time Saturday to pick up the items they discarded in the chaos.
CNN's Michael Martinez in Los Angeles and CNN's Greg Botelho in Atlanta reported and wrote. CNN's Chelsea J. Carter, Casey Wian, Deborah Feyerick, Paul Matadeen, Kyung Lah and Carey Bodenheimer contributed to this report.
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