Authorities are currently investigating a series of letters containing suspicious substances that were sent to multiple congressional offices on Capitol Hill, as detailed in a memo to senior congressional staff. The Senate Sergeant at Arms, in a notice obtained by POLITICO, highlighted ongoing efforts by law enforcement to intercept these letters, although some may still reach their intended destinations.

The investigation involves the Capitol Police, the FBI, and the U.S. Postal Inspection Service. It has been revealed that similar letters have also been dispatched to various lawmaker’s state and district offices across the country.

In a specific advisory to House staff, the substance was described as a “suspicious white powder.” As of now, no members of the House have been confirmed as recipients. The House Sergeant at Arms urged staff to adhere to rigorous mail handling procedures to safeguard against potential harm.

The letters are subject to meticulous screening processes established following the 2001 anthrax attacks, which include off-site locations where mail is irradiated and tested for harmful substances. This protocol notably delayed potential threats previously, including suspected explosive devices in 2018 and a ricin-laced envelope in 2013 intended for Senator Roger Wicker.

Moreover, the National Association of Secretaries of State and the National Association of State Election Directors reported that similar suspicious letters were sent to state election offices and officials. They assured that they are coordinating with law enforcement to protect personnel and facilities, maintaining essential operations despite the threats.

House and Senate mail undergoes processing at two separate facilities in Maryland, where it is screened and tested, a process that can extend delivery up to two weeks. Offices at the state and district level have the option to utilize this security screening for their mail or engage comparable services.

The memo circulated among the staff also included a photo of one of the suspicious envelopes, advising to watch for signs like irregular handwriting or mismatching postmarks and return addresses.

As the investigation continues, all staff are advised to remain vigilant and report any suspicious mail to ensure the safety and integrity of all governmental operations.