About 9:20 a.m. Friday, Ciancia walked up to a Transportation Security Administration checkpoint in Terminal 3. He pulled a .223-caliber assault rifle from a bag and shot TSA officer Gerardo Hernandez "at point-blank range," according to a court document filed by an FBI agent.
Ciancia then went up an escalator but returned to shoot Hernandez again, apparently after seeing him move.
He continued walking and shooting. Witnesses said he went from person to person, asking, "Are you TSA?"
"I just shook my head," traveler Leon Saryan told CNN's Anderson Cooper. "And he kept going."
Hernandez, 39, was the first TSA officer to die in the line of duty since the agency was created in 2001.
"He took pride in his duty for the American public and for the TSA mission," said his wife, Ana Hernandez.
The couple, who married in 1998, have two children.
Two other TSA officers -- James Speer, 54, and Tony Grigsby, 36 -- were wounded but were released from the hospital.
Grigsby, who was shot in the foot, told reporters Monday he was injured while helping an elderly man move to a safe area.
"I turned around and there was a gunman," he said. "Shot me twice."
A traveler who was shot in the leg, 29-year-old Brian Ludmer of Lake Forest, Illinois, was in fair condition Sunday.
The police response
TSA officers are unarmed. So it was airport police officers who eventually shot Ciancia multiple times in the chest, also striking him in the face and neck.
Airport Police Chief Patrick Gannon said the FBI told him that his officers were 60 seconds behind Ciancia. He praised their response, even though he acknowledged that he had moved his officers away from positions inside the checkpoints during the past year.
"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."
Holder said Monday that the investigation will include a review of security measures at LAX and other airports.
"The responsibility for protecting airport security is not a TSA function but something that I think we need to certainly examine, given what happened in Los Angeles," he said.
The incident forced authorities to shut down parts of the airport, evacuate travelers and put a temporary hold on some departures and landings.
More than 167,050 airline passengers were affected by the incident Friday as a result of cancellations, delays or diversions to other airports, according to LAX. One airline, JetBlue, temporarily moved its operations to Long Beach Airport.
On Saturday, an additional 40 flights were affected, including 30 that were canceled, involving about 4,000 passengers, according to Los Angeles International Airport.
According to FlightAware, a flight tracking website, airlines canceled 236 flights into or out of LAX after the incident Friday morning and 27 more Saturday.
An additional 919 flights were delayed over the two days, FlightAware said.
Some of those cancellations and delays may have been caused by problems other than the shooting, however.