From the fine print of the arrest announcement:

This investigation was conducted by the Inland Northwest Joint Terrorism Task Force (INJTTF) comprised of the Federal Bureau of Investigation, the Bureau of Alcohol, Tobacco, Firearms and Explosives, the Federal Air Marshal, the U.S. Border Patrol, the Department of Homeland Security — Homeland Security Investigations, the Spokane Police Department, the Spokane County Sheriff’s Office, and the Washington State Patrol, and with assistance from Stevens County Sheriff’s Office and Washington State Employment Security Department.

Sounds like the suspect might have been living on government-provided unemployment insurance.

UPDATE: Sheryl Hutchison, spokesperson for the Employment Security Department, tells me that her department is a member of the Northwest Joint Terrorism Task Force, and was contacted by the FBI to help find Kevin William Harpham.

“Apparently, our involvement was at a point where the FBI had a name and was trying to find this person," Hutchison said. "They came to us to see if any of our records could help with that search, and apparently the wage records we were able to provide helped them narrow down the search and find him.”

Hutchison said that doesn't necessarily mean Harpham was living on unemployment insurance. Anyone in the state who's covered by unemployment insurance—basically, anyone with a full time job—has a paper trail at the Employment Security Department.