The Capitol Building yesterday (Getty Images)

A letter, addressed to Mississippi Senator Roger Wicker‘s office, tested positive for the toxic poison ricin. According to the Washington Post, the letter was found this morning “at an off-site location where congressional mail has been screened since anthrax-laced letters were sent to Capitol Hill in 2001.”

The mail facility is located in Washington, and a law enforcement told CNN said that the envelope tested positive in a “first routine test,” and then tested positive twice again. It was sent to a lab for more testing. CNN adds, “Sen. Claire McCaskill told reporters after a briefing for lawmakers that a suspect has already been identified in the incident. Members will be warning their home-state offices to look out for similar letters, she said.”

The letter was postmarked from Tennessee. It’s unclear why Wicker was targeted, but he’s been assigned a protective detail. And in case you needed to know more about him, you can read this: “Who is Roger Wicker?“