BURLINGTON, Iowa (AP) — Workers at the Des Moines County Courthouse are sniffing around the 77-year-old building and using blueprints to find the source of a mystery smell. The Hawk Eye reports the sewer-like stench has been wafting around the basement and parts of the third floor, including the jury deliberation room. The unpleasant smell has been noticeable over the past few weeks, though workers say it happens every fall.

Courthouse employees tracked past odors to suspect pipes and busted holes in the building’s walls to seal cracks. Maintenance workers suspect that a pipe in the jury room might be creating the smell. They plan to open the wall after jury trials end this week.

County maintenance supervisor Rodney Bliesener says he’s confident workers will identify the source.