The Douglas County Courthouse, 1100 Mass., was evacuated about noon Tuesday after an employee thought she smelled a “slight amount” of gas in the attic.

It turned out that the smell actually was coming from a dead mouse, County Administrator Craig Weinaug said.

“It’s one of those things where the outcome was humorous, but everybody did what they were supposed to do,” Weinaug said.

An employee from the Register of Deeds office was in the attic looking for records when she noticed the smell, Weinaug said. The fire department and sheriff’s office were called, and the decision was made to evacuate the building, he said.

Firefighters checked the attic and determined the smell was from a dead mouse, although the mouse remains weren’t immediately found.

“You laugh after it’s over, but when it happens you just go into an automatic mode and do what needs to be done,” Weinaug said, adding that someone was going to be sent to find the offending mouse and remove it.