LOS ANGELES >> The 23-year-old charged as the gunman in the 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 told The Associated Press today.

Authorities do not believe the friend knew that Paul Ciancia, the man charged in the attack, 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 more TSA workers, said the official, who is not authorized to speak publicly about the investigation and requested anonymity.

Ciancia was dropped off in a black Hyundai and was not a ticketed passenger. He was able to respond to investigators’ questions at the scene Friday, the official told the AP exclusively.

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 the hospital, the official said. Ciancia was sedated for medical reasons, the official said, adding that one gunshot to the mouth blew a molar out of the suspect’s jaw

Federal prosecutors charged Ciancia on Saturday with murder of a federal officer and committing violence at an international airport. The charges could qualify him for 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 39-year-old TSA officer Gerardo I. Hernandez, killing him.

He then 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 it clear he intended to kill any of them who crossed his path, FBI Agent in Charge David L. Bowdich said.

The shooter’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 "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.

U.S. Rep. Michael McCaul, R-Texas, chairman of the House Homeland Security Committee, said on CNN’s State of the Union on Sunday he had seen the note and said Ciancia’s actions show how difficult it is to protect travelers at a massive airport such as LAX.

The terminals 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.

"It’s like a shopping mall outside the perimeter, it’s almost like an open shopping mall," McCaul said. "So it’s very difficult to protect."

The FBI has served a search warrant on a Sun Valley 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 the rifle used in the shooting was purchased in Los Angeles. Ciancia also had two additional handguns that he purchased in Los Angeles, but which weren’t at the crime scene, a law enforcement official said. The official, who has been briefed on the investigation, was not authorized to speak publicly and requested anonymity.

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

"He didn’t buy them on the street. He didn’t buy them on the Internet," the official said. "He bought them from a licensed gun dealer — the rifle and the two handguns."

Hernandez, a three-year veteran of the TSA, moved to the U.S. from El Salvador at age 15, married his sweetheart, Ana, on Valentine’s Day in 1998 and had two children.

The other two TSA officers wounded in the attack have been released from the hospital.

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

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

The FBI was still looking into Ciancia’s past, but investigators said they had 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.

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Associated Press writers Alicia Chang and Gillian Flaccus in Los Angeles contributed to this report.