(CNN) -- A passenger using a public restroom at El Paso, Texas, International Airport found a bit of a surprise: a gun left behind by a federal agent.

The firearm was found Tuesday morning past the security checkpoints, said Terry Sharpe, the airport's operations manager.

"It was found in the sterile area," he said. "The investigation is still in place and is ongoing with the airport and the TSA."

Sharpe said the weapon was discovered in a women's restroom by a flight passenger, who notified authorities.

"At that point, law enforcement took over," he said.

Sharpe did not disclose further details on the agent who left the gun behind, citing the current investigation.