Authorities in Spokane County, Wash., on Monday arrested 37-year-old Aaron Fairnacci on allegations of starting the Old Trails Fire over the weekend. Photo courtesy Spokane County Sheriff's Office/Facebook

Aug. 4 (UPI) -- Authorities in Washington said late Monday that officers have arrested a 37-year-old man accused of starting one of three wildfires burning in Spokane County that have forced tens of thousands of people to evacuate and destroyed hundreds of structures.

The suspect, Aaron Farinacci, was detained Monday afternoon in Spokane County. He has been charged with one count of first-degree arson. He is being held on $1 million bond.

The Old Trails Fire erupted Saturday at around midnight PDT.

Spokane County Sheriff John Nowels told reporters during a press conference that authorities began investigating the fire when it ignited. He credited local citizens with helping investigators arrest Farinacci.