The 23-year-old charged in a deadly shooting at Los Angeles International Airport told authorities at the scene that he acted alone and had been dropped off by a friend, a law enforcement official who has been briefed on the investigation said Sunday.

Authorities do not think the friend knew that Paul Ciancia, the alleged gunman, planned to open fire inside LAX’s Terminal 3 just moments later, killing one Transportation Security Administration officer and wounding three other people, including two TSA workers, said the official, who is not authorized to discuss the investigation and spoke on the condition of anonymity.

Ciancia was dropped off in a black Hyundai, and he did not have an airline ticket. He was able to respond to investigators’ questions at the scene Friday, the official told the Associated Press.

Ciancia, an unemployed motorcycle mechanic who grew up in the small, blue-collar town of Pennsville, N.J., was shot four times and was under 24-hour armed guard at a hospital, the official said. He was sedated for medical reasons, the official said, adding that one gunshot blew a molar out of the suspect’s jaw.

Federal prosecutors charged Ciancia on Saturday with murdering a federal officer and committing violence at an international airport. He could face the death penalty.

In court documents and interviews, authorities spelled out a chilling chain of events, saying Ciancia walked into the airport, pulled a .223-caliber assault rifle from his duffel bag and fired repeatedly at point-blank range at TSA officer Gerardo I. Hernandez, 39, killing him.

He then allegedly fired on at least two other uniformed TSA employees and an airline passenger, who all were wounded, before airport police shot him as panicked passengers cowered in stores and restaurants, authorities said.

It wasn’t clear why Ciancia targeted TSA officers, but what he left behind made clear that he intended to kill any of them who crossed his path, FBI Agent in Charge David L. Bowdich said.

Ciancia’s duffel bag contained a handwritten, signed letter stating that he had “made the conscious decision to try to kill” multiple TSA employees and that he wanted to “instill fear in their traitorous minds,” Bowdich said.

The letter also talked about “how easy it is to get a gun into the airport,” the law enforcement official said.

House Homeland Security Committee Chairman Michael McCaul (R-Tex.) said on CNN’s “State of the Union” on Sunday that he had seen the note and that the incident shows how difficult it is to protect travelers at a massive airport such as LAX.

The terminals there are open and easily accessible to thousands of people who arrive at large sliding-glass doors via a broad ring road that fronts the facility and is designed to move people along quickly.

The FBI has served a search warrant on a Los Angeles residence where Ciancia lived, Ari Dekofsky, a spokeswoman for the FBI’s Los Angeles field office, said Sunday. Agents are still interviewing people, she said.

Authorities believe that the rifle used in the shooting was purchased in the city. Ciancia bought two additional handguns in Los Angeles, but they were not at the crime scene, another law enforcement official said. The official, who has been briefed on the investigation, was not authorized to speak publicly and spoke on the condition of anonymity.

The purchases appeared legal, although authorities were still tracing them, and it’s unclear whether Ciancia used his own identification or someone else’s, the official said.

“He bought them from a licensed gun dealer — the rifle and the two handguns,” the official said.

Hernandez, a three-year employee of the TSA, moved to the United States from El Salvador at age 15; married his wife, Ana, on Valentine’s Day in 1998; and had two children.

The two TSA officers who were wounded have been released from the hospital.

Brian Ludmer, a Calabasas High School teacher, remained in fair condition at Ronald Reagan UCLA Medical Center with a gunshot wound to the leg. His family declined to comment, hospital officials said.

Two other people suffered injuries trying to evade the gunman but weren’t shot.

The FBI is looking into Ciancia’s past, but investigators said they have not found evidence of previous crimes or any run-ins with the TSA. They said he had never applied for a job with the agency.

— Associated Press