Los Angeles (CNN) -- The suspected Los Angeles International Airport gunman walked up to a security checkpoint, shot a TSA officer "at point-blank range," went up an escalator, then came back down to shoot his victim again, a federal prosecutor said Saturday.
That TSA officer, Gerardo Hernandez, died of his wounds.
The man who shot him, authorities say, is 23-year-old Paul Anthony Ciancia. A federal complaint was filed Saturday afternoon charging Ciancia with two felony offenses -- murder of a federal officer and commission of violence in an international airport, said U.S. Attorney Andre Birotte Jr..
If convicted, Ciancia would face life in prison without parole or the death penalty, according to the federal prosecutor. The U.S. attorney general would decide if a death sentence would be sought.
According to Birotte, the suspect walked up to a TSA checkpoint in Terminal 3 around 9:20 a.m., pulled a "Smith & Wesson .223-caliber M&P15 assault rifle out of his bag and filed multiple rounds" at the uniformed officer.
He walked away, went up an escalator, then came back down to fire more shots at Hernandez, Birotte said. The gunman then proceeded through the terminal -- hitting two other uniformed TSA officers and a civilian passenger with gunfire, said Birotte -- before he was shot and wounded himself by airport police.
By then, people were sprinting for their lives -- down escalators, out emergency exit doors, cramming into bathrooms and first-class lounges, anything to get out of the line of fire.
Two people suffered what FBI Special Agent in Charge David Bowdich called "evasion injuries," getting hurt as they were trying to avoid being shot.
Ciancia is being treated in a hospital after being shot himself by airport police, Bowdich said late Saturday afternoon.
"He is unresponsive," the FBI official added, "and we are unable to interview him, as of today."
'Conscious decision to kill ... TSA employees'
So how did he ended up handcuffed to a gurney, leaving behind five magazines of ammunition that Los Angeles Mayor Eric Garcetti said "could have literally killed everyone in that terminal"?
Some clues have emerged -- including that authorities found he'd been carrying a rant that appeared to refer to the New World Order plus 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 is conspiring to form an authoritarian, one-world government.
Bowdich, from the FBI, said the handwritten note indicated the suspect made "a conscious decision to kill multiple TSA employees."
"He addressed them (TSA officers) at one point in the letter," Bowdich said, "and stated that he wanted to 'instill fear into their traitorous minds.'"
In his diatribe, the gunman claimed the TSA treats Americans like terrorists even though all people aren't equally dangerous, a U.S. law enforcement official said.
And near the end of the note was a derogatory reference to Janet Napolitano, the former head of the Department of Homeland Security that includes TSA, according to the same official.
Another clue to the state of mind of Ciancia -- who was dropped off at the airport by a roommate who, investigators believe, didn't know about any shooting plot, the law enforcement official said -- 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."
Widow of victim: 'I am truly devastated'
Ciancia is being treated for his injuries at Ronald Reagan UCLA Medical Center, according to an intelligence source. So, too, is one other person -- the hospital said Saturday one person is in critical condition and the other is in fair, without specifying their names, and noted another person was treated and released Friday.
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 said Friday.
It's presumed that fatality is Gerardo Hernandez, the lone person killed in the shooting according to authorities.
He's the first TSA officer to die in the line of duty since the agency was founded in 2001. The late officer was working as a travel document checker at the time, TSA workers' union and federal sources say.
Gannon said airport police quickly applied first aid to Hernandez, put him in a wheelchair, then rolled him to an ambulance.
"They were absolutely committed to trying to save a life," the police chief said. "Unfortunately, that didn't work out."
Gerardo Hernandez would have turned 40 next week. His widow described him as a "wonderful husband, father, brother, son and friend."
"I am truly devastated," his widow said.
The chaos also affected more than 165,000 passengers on hundreds of flights, as the airport shut down for hours. By early Saturday afternoon, all of it -- including Terminal 3 -- was reopened.
By then, security was out in force -- an "enhanced deployment" that included Los Angeles police department officers and air marshals in addition to airport police, according to Airport police Chief Patrick Gannon. Some were uniformed, others were undercover.
"For today and for the foreseeable future, we'll continue (to have) a very high profile at the curbs and anywhere in those ticketing areas and anywhere on our campuses," the chief said.
Questions about recent repositioning of airport police
The shooting has stirred questions about a recent repositioning of airport police officers around what is known as LAX.
Gannon explained Saturday that, in the past year, he decided to move officers from behind a TSA security checkpoint to in front of it, where they also took on "greater responsibilities" such as monitoring both the arrival and departure floors of the terminal.
"The threat ... at the airport does not exist behind security at that podium, the threat exists from the curbline on," Gannon said. "So ... we have our people stationed throughout the airport.
"That particular individual" -- he added, referring to the nearest police officer to the site of Friday's initial shooting -- "was just moved to the front part of the airport."
At the same time, Gannon acknowledged the trade-off of having the officers roam a larger area, rather than sit at a checkpoint.
"So are they going to be in the exact same (place), exactly where I'd hoped they would be? No," he said. "It didn't happen in this particular case."
Was there anything more behind the shift? A law enforcement source told CNN on Saturday that airport police officers had complained to their union about being "bored with the assignment" of being stationed behind the TSA checkpoint.
Concurrently, TSA management complained that airport police officers weren't paying attention -- sometimes perusing their phones, using iPads or reading books on the job -- according to the same source.
Then came "a fix" agreed to by TSA and airport police management, to keep officers in the public areas but position them in front of the checkpoints, including the one where Friday's shooting began. Part of the deal was that officers would never be more than two minutes from the checkpoint screening area, if needed, according to the law enforcement source.
While Gannon hasn't addressed the claims of "bored" and "distracted" officers, he said Saturday the FBI has indicated his officers "were 60 seconds behind the suspect." However it was decided where they'd be standing, he insisted the two were where they were supposed to be, and did what they were supposed to do.
"Our officers were deployed where they were supposed to be and performed heroically in this particular matter," Gannon said.
TSA Administrator John Pistole called the shooting "a significant event" that will prompt a review of security protocol with partner agencies.
Speaking Saturday from Los Angeles, Pistole said,"This gives us great concern, so we'll look at what our policies are."
CNN's Dan Simon in Los Angeles and CNN's Greg Botelho in Atlanta reported and wrote. CNN's Lateef Mungin, Michael Martinez, Evan Perez, Joe Sutton, Chelsea J. Carter, Casey Wian, Deborah Feyerick, Paul Matadeen, Kyung Lah and Carey Bodenheimer contributed to this report.