Note about the content "HA HA" and white powder. Such letters were sent to congressmen.

Matthew Unglesbee, a 37-year-old from Quincy, Illinois, faces charges for sending threatening letters containing a suspicious white substance to members of Congress. The FBI received an anonymous tip about his actions, which included four letters with handwritten notes saying 'HA HA'. The letters were sent from Springfield, Illinois, and Unglesbee admitted to sending them after hearing a conversation about similar incidents. He expected the recipients to take the threats seriously and call in hazardous materials teams, believing the substance could be anthrax.