The 37th District Court in Warren was evacuated Monday morning when a suspicious white powder was found in an envelope.
Four people were taken to a hospital to be tested for exposure to any hazardous materials, but were not immediately showing any signs of illness.
The letter was delivered by mistake to the courthouse and was sent back to the post office. It arrived again undeliverable to the courthouse and was opened by an employee.
The courthouse, which is at 833 Common Road -- near Van Dyke and 12 Mile Road -- was closed for the day.