Rep. Bennie Thompson, D-Miss., the House committee chair investigating the Jan. 6 attack on the U.S. Capitol, received a threatening letter at his office in Washington, D.C. on Tuesday, ahead of the next scheduled panel hearing on Oct. 13. The Capitol Police said a letter sent to Thompson included “concerning language,” and prompted evacuations. Eventually, the police declared an “all clear,” as the letter contained nothing harmful, but investigators still want to know who and why the letter was sent. “We just screened (the letter) and determined it not to have anything dangerous inside. Powde…