WASHINGTON (AP) — A federal probe of a Transportation Security Administration program to screen suspicious behavior of passengers at airports suggests the effort, which has cost almost $1 billion since 2007, has not been proven effective, according to a report released Wednesday.

The Government Accountability Office said its investigation found that the results of the TSA program — called Screening of Passengers by Observation Techniques — were “no better than chance.” Under the program, agents identify suspicious looking people and talk to them to determine whether they pose a threat. The investigators looked at the screening program at four airports, chosen on the basis of size and other factors.