After killing that officer, Ciancia fired on at least two other uniformed TSA employees and a civilian airline passenger, who were all wounded. Airport police eventually shot him as panicked passengers cowered in stores and restaurants.
Ciancia's duffel bag contained a handwritten letter signed by Ciancia stating he'd "made the conscious decision to try to kill" multiple TSA employees and that he wanted to stir fear in them, said FBI Special Agent in Charge David L. Bowdich.
The bag also had five magazines of ammunition.
Federal prosecutors filed charges of first-degree murder and commission of violence at an international airport against Ciancia. The charges could qualify him for the death penalty.
The FBI was still looking into his past, but said they had not found evidence of past crimes or any run-ins with TSA. They said he had never applied for a job with TSA.
Authorities believe someone dropped Ciancia off at the airport. Agents are reviewing surveillance tapes to piece together the exact sequence of events, he said.
"We are really going to draw a picture of who this person was, his background, his history. That will help us explain why he chose to do what he did," Bowdich said. "At this point, I don't have the answer on that."
The note found in the duffel bag suggested Ciancia was willing to kill almost any TSA officer.
"Black, white, yellow, brown, I don't discriminate," the note read, according to a paraphrase by a law enforcement official briefed on the investigation. The official spoke on the condition of anonymity because he was not authorized to speak publicly.
The suspect's screed also mentioned "fiat currency" and "NWO," possible references to the New World Order, a conspiracy theory that foresees a totalitarian one-world government.
Terminal 3, the area where the shooting happened, reopened Saturday. Passengers who had abandoned luggage to escape Friday's gunfire were allowed to return to collect their bags.
The TSA planned to review its security policies in the wake of the shooting. Administrator John Pistole did not say if that meant arming officers.
As airport operations returned to normal, a few more details trickled out about Ciancia, who by all accounts was reserved and solitary.
Former classmates barely remember him and even a recent roommate could say little about the young man who moved from New Jersey to Los Angeles less than two years ago. A former classmate at Salesianum School in Wilmington, Del., said Ciancia was incredibly quiet.
"He kept to himself and ate lunch alone a lot," David Hamilton told the Los Angeles Times. "I really don't remember any one person who was close to him .... In four years, I never heard a word out of his mouth."