Transportation Security Administration workers were mourning Friday the first worker's death in the line of duty since the agency was created in the aftermath of the Sept. 11 attacks.
A TSA behavior-detection officer, whose job was to spot suspicious activities to deter possible terrorist plots, was shot to death at Los Angeles International Airport by a gunman authorities identified as Paul Ciancia, 23.
Three other TSA officers were also shot and wounded in the incident, according to David Cox, president of the American Federation of Government Employees, the union representing TSA workers.
"It's with a very, very sad heart that I inform you that one of our own has lost his life today," Cox said. "To our knowledge, he was the first (TSA officer) to die in the line of duty."
TSA officials didn't respond Friday to repeated requests for comment about the shooting.
Rand Beers, acting secretary of the Department of Homeland Security, which oversees TSA, said the department would work with law enforcement to investigate "this heinous crime."
"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," Beers said.
Rep. Michael McCaul, R-Texas, the chairman of the Homeland Security Committee, said he was assured that the investigation into why the shooter "carried out this horrendous attack at one of the largest airports in the country will be thorough."
"I commend the work of the Transportation Security and law enforcement officers who took immediate action to pursue and subdue the shooter," McCaul said. "These officers reportedly underwent training for this type of incident just weeks ago, and their professionalism, expertise and bravery undoubtedly saved many lives."
Sen. Jay Rockefeller, D-W.Va., the chairman of the transportation committee, commended TSA agents for protecting people.
"TSA agents are at the front lines of protecting our nation, and they deserve our support in carrying out risky and sensitive jobs," Rockefeller said. "While some in Congress believe that privatizing our aviation security workforce would be preferable, these brave men and women are proving that the federal TSA agents are highly capable and ready to protect passengers every step of the way."
US Airways tweeted: "We appreciate the work our TSA colleagues do each day to keep us safe."
The FBI doesn't break out statistics on assaults against TSA workers. But more than 1,000 federal law-enforcement officers are assaulted each year, and several are killed in the line of duty.
From 2007 to 2011, the FBI counted 8,375 assaults against federal officers, with seven deaths.
Assaults are also common on TSA officers, occurring daily with perhaps thousands of cases every year, Cox said.
While officers are trained to defuse volatile situations, TSA officers are unarmed and don't have the authority to arrest people. Local police officers arrest suspects at checkpoints, when necessary.
"I'm not sure other than armed police that anyone is prepared to deal with someone that pulls out a gun and begins shooting at you," Cox said. "That's a tough situation."
While TSA officers aren't asking to carry firearms, Cox said they would like to be able to arrest suspects.
"These people will assault the officers and walk away, and our officers can't make an arrest," Cox said. "But certainly we would like to have our officers be able to do arrests."
Los Angeles airport has 2,157 TSA workers, although Cox couldn't say how many are typically stationed in Terminal 3, where the shooting occurred.
He suggested that airports would be safer if security were fully staffed. But he warned that federal budget cutting has restricted TSA hiring.
"All government agencies are seeing constant cutbacks," Cox said. "Austerity is killing us."