The King County District Courthouses in Issaquah and Redmond shut down Monday after receiving mail containing a suspicious white powder. The powder was not harmful, according to tests by the Eastside Fire and Rescue Hazardous Materials Team.

“A ‘nonhazardous household powder’ is what we’re calling it,” United States Postal Inspector Jeremy Leder said.

The Issaquah courthouse discovered the powder, which arrived in a plain white envelope with ineligible writing on the back, around noon. Issaquah police assisted in the investigation, according to the city of Issaquah’s Twitter account.

Around 1:30 p.m., the Redmond courthouse opened its mail and discovered an unknown powder in a similar envelope. The powder also tested as nonhazardous. The court closed for the remainder of the day.

Federal postal inspectors are now attempting to track where the letters entered the mail system, Leder said.

“Obviously, whoever did this was trying to cause some kind of commotion,” he said.

Leder said that the Postal Inspection Service, the law enforcement branch of the United States Postal Service, investigates questionable packages all the time. But he estimated Seattle-area inspectors only see clearly intentional cases like the ones in Issaquah or Redmond once or twice a year.

“It’s pretty rare, it doesn’t happen very often,” he said.