The U.S. Department of Homeland Security searched a hangar at Boulder Municipal Airport on Monday afternoon, although officials aren’t saying what the federal agency is investigating.

A man who identified himself as a Homeland Security agent declined to discuss the search of Hangar 3355 at the airport. At least four airplanes and five vehicles were visible through an opening in the hangar, which is located on the southeast side of the airport.

A Boulder County sheriff’s K-9 unit was on hand briefly to assist with the search. The dog, named Titan, was taken inside the hangar for about 10 minutes and could be heard barking before the deputy and dog left the scene.

The Homeland Security agent — who arrived in a black, unmarked Jeep and was not wearing a uniform — left about 10 minutes after the deputy. He said he could not discuss the nature of the search. He left carrying a small bundle of papers.

Sheriff’s Cmdr. Rick Brough said the department provided K-9 assistance, but he declined to discuss the details of the operation. He said that Titan, a German shepherd, is a dual-purpose police dog that’s trained in patrol work and narcotics detection.

He referred other questions to Homeland Security.

Calls to an area Homeland Security representative were not returned Monday. Airport manager Tim Head also did not respond to calls for comment. He was not in his airport office at the time of the search.

Boulder police also aren’t discussing the case, but it appears the agency is involved.

Kim Kobel, a police spokeswoman, said in an e-mail Monday afternoon, “This is a Homeland Security case and we have been asked not to discuss it.”

A police call log shows that Boulder officers responded to an “outside agency assist” at 5:55 p.m. Saturday at the airport, but officials on Monday refused to release a copy of that report.

Of the four aircraft that were visible inside the hangar, two had visible tail numbers. Both of those planes are registered to the Soaring Society of Boulder.

The nonprofit club has been in continuous operation since 1959, according to the Soaring Society’s website. The group provides gliders, towing and training.

One of the planes is a fixed wing single-engine Piper PA-18-150 built in 1962, according to records with the Federal Aviation Administration. The other plane is a single-engine Piper PA-25-235 built in 1971.

Alfonso Ossorio, an instructor with the Soaring Society of Boulder, said Monday afternoon that he wasn’t aware of the Homeland Security search.

“Maybe they got some sort of tip,” he said, noting that the club only operates two of the four airplanes in the hangar.

He said there is a crop duster airplane among the parked aircraft, although the device for spraying crops has been removed.

He said the club was towing gliders earlier in the day and nothing was out of the ordinary. He said he does not know the owners of the other aircraft inside the hangar.

“It’s a long tube hangar, basically,” he said. “Everybody has their own door to access their aircraft to pull it out. Somebody else could walk over to another airplane.”

Contact Camera Staff Writer Heath Urie at 303-473-1328 or urieh@dailycamera.com.