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Des Moines police say no harmful substances were found after threatening letter with white powder in it was opened at the Federal courthouse in downtown Des Moines Monday morning.

Police say they received a call at dispatch at 1:46 p.m. after a receptionist on the second floor of the courthouse opened a letter that had white powder substance in it. There was a note in the envelope that contained a threat and identified the substance as toxic. She contacted her supervisor and then police were notified.

Des Moines HazMat was called to the courthouse at East First and Court Avenue and was able to determine the substance was acetaminophen – a common over the counter pain medicine.

U.S. Postal Inspectors are taking over the case because the threat was mailed and Des Moines police say the inspectors may have linked it to a case they are already looking into.