Federal authorities investigate suspicious letters sent to congressional offices

The FBI, the United States Postal Inspection Service, and the Capitol Police are investigating letters containing suspicious substances that were mailed to congressional offices. According to the New York Post, internal emails sent to Capitol Hill staff on Thursday disclosed the ongoing multi-agency investigation. [1]

The official warning distributed to congressional staff included a photograph of one of the envelopes. According to the New York Post, the envelope was postmarked with the acronym DSA and listed a return address located in the same Financial District building that the Democratic Socialists of America previously used on its membership forms. [1]

The Democratic Socialists of America is a broad political organization on the left wing of the spectrum focused on democratic socialism. It represents the largest socialist organization in United States history, counting more than 120,000 members as of July 2026. [3]

In the United States, capitol police agencies provide security services for legislative bodies and state agencies. The federal Capitol Police agency works alongside federal law enforcement partners during investigations on Capitol Hill. [1][2]