LOS ANGELES - A 23-year-old man at Los Angeles International Airport pulled an assault rifle out of his bag and shot his way through a security checkpoint Friday, killing a TSA screener and wounding at least two other officers as panicked passengers fled.

LOS ANGELES — A 23-year-old man at Los Angeles International Airport pulled an assault rifle out of his bag and shot his way through a security checkpoint Friday, killing a TSA screener and wounding at least two other officers as panicked passengers fled.

A number of people were injured, including two who were shot and wounded and others hurt in the pandemonium.

Nearly 750 flights were halted, grounded, or diverted as police evacuated passengers and shut down three terminals.

Authorities found a note in the gunman’s bag indicating that he wanted to kill TSA agents, according to two law enforcement officials.

The note contained other anti-government rhetoric and made clear that he wanted to avoid hurting civilians, the officials said.

The gunman, identified by the FBI as Paul Ciancia, 23, of Los Angeles, made his way deep into the airport before he was wounded by police. He is in critical condition at Ronald Reagan UCLA Medical Center and in custody, officials said.

The slain screener was the first killed in the line of duty since the Transportation Security Administration was created after the terror attacks on Sept. 11, 2001. He was identified late Friday as Gerardo Hernandez, 39.

The notion of a gunman firing a semiautomatic rifle at security screeners at a major airport just weeks before the holiday season struck a nerve across the country.

It took the nation’s third-busiest airport to a near standstill and disrupted global airline schedules.

Many arriving flights were diverted to other airports and officials advised passengers booked on afternoon flights to just stay away.

In the confusion, passengers wandered around the airport grounds looking for their baggage, or for a relative who had come to meet them, or a vacant hotel room to stay in until flights resumed.

Police said they believe Ciancia, who originally is from Pennsville, N.J., acted alone.

They said they don’t know much yet about his motive, but authorities said they don’t believe it was part of any organized terror attack.

The Pennsville police chief said Friday night that Ciancia’s family had feared that Ciancia was considering suicide.

Chief Allen Cummings said that Ciancia’s father called police on Friday saying that a sibling had received a text message from Ciancia mentioning suicide.

The chief called Los Angeles police to request that they check on him.

“There were two roommates, and they said he was there yesterday but not today,” Chief Cummings said.

The shooting at LAX underscored the vulnerability of airport hubs despite a steady escalation of security over the past decade, even as travelers have grown accustomed to taking off their shoes in screening lines, undergoing full body scans, and ditching their bottled water.

Los Angeles Airport Police Chief Patrick Gannon said his officers and a “couple hundred” Los Angeles police officers practiced a drill about three weeks ago dealing with a scenario very similar to what unfolded Friday.

The shooting began around 9:20 a.m. Los Angeles time, when Terminal 3 was so crowded that there were no vacant seats in the food court.

Chief Gannon said the shooter pulled the rifle from his bag and started firing as soon as he walked into the airport. He kept shooting as he went through the checkpoint and advanced toward the departure gates and restaurants.

As bullets flew, panic erupted.

Passengers huddled in restrooms and restaurants, hoping the gunman would not come in. Some escaped the terminal through emergency exits and hid beneath the bellies of planes waiting on the tarmac.

Some travelers threw themselves to the ground on orders from the police, then rushed in every direction, shouting “Run, run!” from what they believed could be a terrorist attack.

Vernon Cardenas of West Hollywood, Calif., told the Los Angeles Times that the scene was “mayhem,” as frantic parents searched for their children and many people cried.

“Sitting down, all of a sudden, literally just out of the blue, you hear a rumble in the background and a couple of seconds later, people are running at me,” he said.

Many passengers dropped their bags as they rushed away from the terminal, leaving police officers with hundreds, if not thousands, of bags that they needed to screen.

After the suspect was arrested, thousands of passengers milled outside Terminals 2 and 3 as a police bomb squad arrived.

Airport officials said it would take several hours for flights to resume on a normal schedule.

At a news conference Friday evening, Los Angeles Mayor Eric Garcetti said the gunman had at least 100 rounds “that could have literally killed everyone in that terminal.”

In Washington, President Obama said he was “concerned” about the airport shooting, but he declined to comment further.

“I’ll let the law enforcement folks talk about it directly.”

Rand Beers, acting secretary of the Department of Homeland Security, expressed his sympathy for the TSA employee who was killed and those who were injured.

“This act of violence reminds us of the risks the brave men and women of TSA face every day as they work to protect the traveling public,” he said.

The shooting raises questions about how secure the airport screening process is more than a decade after the Sept. 11 attacks.

Last year, a Department of Homeland Security inspector general’s report found that while the TSA has a system to track some security breaches, there is no centralized program that tracks all breaches.

At the six airports visited, the report said, investigators found several lapses.

The review found documentation of “corrective actions” for only 53 percent of the breaches it identified. The report cited several instances of improper screening.

But none of those scenarios addresses an incident like Friday, in which the shooter opens fire in the terminal well before approaching the screeners, and then is able to shoot his way through.