From the FBI:
On Wednesday, the Oregon State Public Health Laboratory completed the preliminary testing of a sample of letters received, including the letter mailed to Grant County. That preliminary testing showed that there were no biological toxins or powders included in or on the letters or envelopes that were mailed to local law enforcement offices.
The FBI and U.S. Postal Inspection Service are in the process of completing their portion of the investigation. Unless new information surfaces, neither the FBI nor the U.S. Postal Inspection Service anticipate pursuing federal charges in this case.