A man was charged with allegedly sending letters with white granular substance, which turned out to be salt, to four members of Congress, according to a criminal complaint unsealed on Monday in federal court in Springfield, Illinois.

He was allegedly heard about reports of other letters with suspicious substances being sent to senators and secretaries of state around the country, the court documents said.

Matthew Unglesbee allegedly sent the letters to four members of Congress in the Northern District of Illinois, including the office of one U.S. senator, according to the Justice Department.