OKLAHOMA CITY - HazMat has given the "all clear" after a letter was found with white powder at the federal building downtown Monday.
Officials have not confirmed who may have sent this letter.
They said a worker opened a package in the mail room and found a letter inside containing the white powder.
Last week three letters were found at Oklahoma government buildings all with a white powder inside.
Authorities determined an inmate sent those letters and the substances were not a threat.