An inmate in a Missouri jail is suspected of sending a threatening letter to authorities in Iowa. The letter forced the shut-down of the main police station in Iowa’s largest city for 20 minutes on Monday as a Des Moines HAZMAT team scoured the area where the envelope was opened. The powder inside was determined to be harmless. It was a combination of paint chips and antacid pills, like Tums.

Investigators say the letter, which contained threats, was sent from a regional jail facility in Pattonsburg, Missouri, which is used to ease overcrowding at the Polk County Jail here in Des Moines.

The inmate’s name hasn’t been released but police say the same person, or someone using his name, sent a threatening letter to the county attorney last week. As yet, no charges have been filed.