TSA officer Gerardo Hernandez was killed

After a weekend of intense investigation, authorities are piecing together more details about Friday's fatal shooting at Los Angeles International Airport, including the suspect's behavior earlier in the week and a warning from his family that may have come moments too late. Police officers arrived at Paul Ciancia's apartment less than an hour after the alleged gunman left for the airport, investigators say.

Here is a rundown to get you up to speed:

THE SUSPECT

Ciancia, 23, of Los Angeles is charged with murder of a federal officer and commission of violence in an international airport.

He was shot by officers Friday and was in critical condition at Ronald Reagan UCLA Medical Center on Sunday.

A source said Ciancia was unable to speak to investigators.

CLUES ABOUT A MOTIVE

A note found on Ciancia indicated that he wanted to kill Transportation Security Administration employees to "instill fear into their traitorous minds," FBI Special Agent in Charge David Bowdich said.

According to someone who knew Ciancia and his three roommates well, Ciancia began asking for a ride to the airport days before the shooting. He claimed he needed to fly to New Jersey to help his sick father, but he never said what day he needed to leave, the source said.

On Friday, Ciancia burst into a roommate's room and demanded a ride to the airport immediately, said the source, who spoke to CNN on condition of anonymity.

The roommate obliged. Investigators don't think the roommate had any idea of Ciancia's plans.

THE NEAR SAVE

Around the same time, Ciancia was sending text messages to family members in Pennsville, New Jersey.

He has no known history of mental illness, but he said in the texts that he was unhappy. And one message suggested something bad would happen.

That alarmed Ciancia's father enough to call Pennsville Police Chief Allen Cummings, who in turn called Los Angeles police and asked them to check on Ciancia.

Perhaps 45 minutes after Ciancia left for the airport, officers arrived at his apartment, said Rep. Michael McCaul, R-Texas, chairman of the House Homeland Security Committee. The two roommates at home did not know where Ciancia and the other roommate had gone.

THE ATTACK

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."

THE VICTIMS

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," his wife, Ana Hernandez, told reporters.

The couple, who married in 1998, had two children.

Two other TSA officers -- James Speer, 54, and Tony Grigsby, 36 -- were wounded but were released from the hospital.

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.

Airport Police Chief Patrick Gannon said the FBI told him 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."

TRAVEL DELAYS

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.

The airport was operating normally Monday morning.

WHAT'S NEXT?

If convicted, Ciancia could face the death penalty or life in prison without parole. The U.S. attorney general would decide whether to pursue a death sentence.

TSA Administrator John Pistole said the shooting has prompted a review of security protocol with partner agencies.

McCaul said better coordination with local law enforcement could improve security at checkpoints.

But the congressman acknowledged that "it's very difficult to stop these types of attacks."

"It's almost like an open shopping mall," he said.