WASHINGTON — A man has been charged in Illinois with mailing four letters containing a white granular substance to members of Congress, all of which were sent in envelopes containing his name and home address.

Matthew Unglesbee has been charged with sending threatening letters containing a white granular substance to three members of Congress, along with a handwritten letter that read “HA HA.” A fourth letter with a white granular substance included the note “HAH enjoy the gift.”

Unglesbee is facing two charges: false information and hoaxes, and mailing threatening communications. He will make an initial appearance in court on Monday afternoon.

In an interview with FBI personnel on Sunday, Unglesbee allegedly admitted that he mailed four letters to four members of Congress after hearing about other letters mailed earlier in the month. The FBI is separately investigating letters containing suspicious substances that were sent to members of Congress and elections officials in recent weeks.

Unglesbee admitted that he knew that people would perceive the letters as dangerous, the FBI says. He said in the FBI interview that the granular substance was salt, which he said “kind of looks like” anthrax. He denied involvement with prior mailings.

A search of his residence turned up a fifth unmailed and empty envelope that was addressed to a member of Congress, according to the FBI.

The case began after an anonymous online tipster told the FBI that they overheard Unglesbee talking about mailing a suspicious substance to members of Congress. The tip was received on Oct. 16, and the FBI responded when the letters showed up to the offices of members of Congress three days later.