SPRINGFIELD, Ill. (AP) — A 37-year-old Illinois man is charged with sending threatening letters to members of Congress containing a white powder, including one with a note reading “HAH enjoy the gift,” according to federal court records.

The criminal complaint unsealed Monday claims Matthew Ungelsbee sent at least four plain white envelopes with a powdery substance to elected officials in Chicago. They were postmarked in Springfield, Illinois, on Oct. 19 and had Unglesbee's name handwritten in the return address section.

Unglesbee, of Quincy in southwestern Illinois, is charged with mailing threatening communications and perpetrating a hoax. He was scheduled to appear in court Monday afternoon. Court records did not list a defense attorney, and a phone number for Unglesbee could not be found. A Facebook message to a Matthew Unglesbee in Quincy was not immediately returned.

FBI agents interviewed Unglesbee at his home on Sunday and he told them all the letters contained salt, court records show. He claimed he’d sent the letters after hearing someone talk about similar mailings in the news earlier this month.

Testing confirmed the white substance was not dangerous. The records did not identify the substance.

A motive was unclear. But Unglesbee said he knew the congress members would “take it serious” because the powder might be perceived as anthrax, which he knew was dangerous and could prompt a response by hazmat teams, according to the complaint.

“Unglesbee claimed he was joking but recognized the recipients would not know he was joking and could perceive it as a threat,” the complaint stated.

Investigators said none of the recipients opened the letters. The most recent envelope was received Oct. 23 at the office of a U.S. senator, records show. It contained a white powdery substance and a handwritten note reading “HAH enjoy the gift,” according to the documents.

The investigation began after an anonymous tipster reported overhearing Unglesbee in a restaurant talking about mailing a suspicious substance to members of Congress. The tip was received Oct. 16, and the FBI tracked Ungelsbee down after the envelopes arrived at the congressional offices days later.

The recipients of the mailings were not named. Authorities searched Unglesbee's home and found a fifth envelope addressed to another congress member's Washington, D.C., office, the records show.

Earlier this month, federal authorities said they were investigating letters with “suspicious substances” that had been mailed to congressional and election offices nationwide. That investigation by the FBI, the U.S. Postal Inspection Service and U.S. Capitol Police was first disclosed in a message from the Senate Sergeant at Arms obtained Oct. 15 by The Associated Press.

Unglesbee denied involvement in those mailings.