Update:A spokesman for Sen. Shelby says:"The Capitol Police are investigating a suspicious package delivered to our front office... I have no further information at this point, but will follow up when I do."
FBI's response to reports of suspicious letters arriving at government offices:
A second letter containing a granular substance that preliminarily tested positive for ricin was received at an offsite mail screening facility. The envelope, addressed to the President, was immediately quarantined by U.S. Secret Service personnel, and a coordinated investigation with the FBI was initiated. It is important to note that operations at the White House have not been affected as a result of the investigation.Additionally, filters at a second government mail screening facility preliminarily tested positive for ricin this morning. Mail from that facility is being tested.Any time suspicious powder is located in a mail facility, field tests are conducted. The field and other preliminary tests can produce inconsistent results. Any time field tests indicate the possibility of a biological agent, the material is sent to an accredited laboratory for further analysis. Only a full analysis performed at an accredited laboratory can determine the presence of a biological agent such as ricin. Those tests are currently being conducted and generally take 24 to 48 hours.The investigation into these letters remains ongoing, and more letters may still be received. There is no indication of a connection to the attack in Boston.