A new report casts strong doubt on the effectiveness of one of the government’s main tools for recognizing potential terrorists before they board airplanes: the Transportation Security Administration’s behavior-detection program.

Stephen M. Lord, a managing director with the Government Accountability Office, told a House Homeland Security subcommittee Thursday that there is no solid evidence that the TSA techniques are effective.

Overshadowing the transportation security subcommittee hearing was the Nov. 1 killing of a TSA employee. Gerardo Hernandez was slain and two other employees were wounded by a gunman who expressed hatred, for no apparent reason, of the agency.

TSA behavior-detection officers (BDOs) did not have a chance to notice anything strange about the alleged shooter, Paul A. Ciancia. The attack, TSA Administrator John S. Pistole said, happened within seconds of the the suspect entering the airport, and there were no BDOs at that location.

But the question before Congress was: Are their techniques really effective?

GAO doesn’t think so.

“Until TSA can provide scientifically validated evidence demonstrating that behavioral indicators can be used to identify passengers who may pose a threat to aviation security, the agency risks funding activities that have not been determined to be effective,” according to a GAO report released before the hearing.

Pistole defended the program, telling the panel that the detection officers “provide a crucial layer of security.”

Pistole’s testimony did not convince Rep. Bennie Thompson (D-Miss.), the ranking member on the full committee. A longtime opponent of the program called SPOT (Screening of Passengers by Observation Techniques), Thompson wants to strip its funding, which has totaled nearly $900 million since 2007.

“Given the limited post-sequester dollars available for transportation security activities, we do not have the luxury of spending hundreds of millions of dollars per year on programs for which TSA cannot prove the effectiveness of or scientifically validate,” he said.

In a change from regular order, Thompson — a strong friend of TSA employees — sounded like Republicans who are more likely to consider government programs unnecessary.

The Republican chairman of the subcommittee, Rep. Richard Hudson (N.C.), is not ready to dump the program. “I don’t think we need to eliminate the capability to do behavioral detection,” he said after the hearing. “I think the question is, are we using it in the most cost-effective and most effective way to stop terrorist threats?”

If Thompson got his way, what would happen to the behavior-detection officers? Would they be fired? Would they by moved to other jobs? If they became regular transportation security officers, would that bring a cut in pay and rank?

These important questions were unasked and unanswered, which leaves the 3,000 BDOs uneasy. No one spoke for them at the hearing. The employee viewpoint was absent.

“BDOs across the country worry about what’s going to happen to them,” BDO Kimberly Kraynak-Lambert said in a telephone interview. She is president of American Federation of Government Employees (AFGE) Local 332 at Pittsburgh International Airport. “These are people just trying to do their jobs and keep people safe.”

But is what they do keeping people safe?

The evidence GAO reviewed doesn’t say so.

“Available evidence does not support whether behavioral indicators can be used to identify aviation security threats,” says the GAO report. It follows a Department of Homeland Security (DHS) inspector general report about SPOT issued in May. That report said, “TSA cannot ensure that passengers at United States airports are screened objectively, show that the program is cost-effective, or reasonably justify the program’s expansion.”

Pistole, a former FBI agent, countered by citing a study from DHS, TSA’s parent department, and drawing on his 30 years of law enforcement experience. “I can personally attest to the effectiveness of behavior detection principles,” he said.

His written statement pointed to a validation study American Institutes for Research did for DHS. It found that “a high-risk traveler is nine times more likely to be identified using behavioral detection versus random screening.”

Lord said problems with the DHS study made it unreliable as an indicator of SPOT’s effectiveness.

For Kraynak-Lambert, this is about more than competing studies.

“I’ve been a BDO for six years, and I think it is one of the best programs TSA has,” she said. “I believe the SPOT program is highly effective because of my personal experiences as a BDO.” She wouldn’t share those experiences, saying she can’t discuss classified information.

AFGE National President J. David Cox Sr. acknowledged that the program is not perfect but said it should be fixed, not abolished. In a conference call with reporters, Cox renewed his call for a new class of transportation security officers, a group that would be armed and have law enforcement arrest powers. Cox said that “a larger and more consistent armed presence in screening areas would be a positive step in improving security” for TSA employees and the flying public.

Hudson disagrees, saying the law enforcement role should remain with local authorities.

“I don’t think that’s a good use of our resources,” he said.

Twitter: @JoeDavidsonWP

Previous columns by Joe Davidson are available at wapo.st/JoeDavidson.