GRAND RAPIDS, Mich. (WOOD) — A man already in prison has been sentenced to almost another decade behind bars for sending threatening letters, including one to the U.S. District Court in Kalamazoo, claiming it was covered in anthrax, the U.S. Attorney’s Office said.

Nathon James Zink, 35, was sentenced to nine years and four months in federal prison, said the attorney’s office. He was charged in February for two counts of mailing threatening communications, including one to a federal employee. He pled guilty to both counts in March.

According to the Michigan Department of Corrections, Zink has been in prison since January of 2010 for other crimes including home invasion, arson and unlawful possession of firearms. His sentence for sending the threatening letters will be served after he is finished serving his current sentences.

On Aug. 20, 2020, Zink mailed a note from prison through the U.S. Postal Service addressed to K.B. at a known address in Paw Paw, Michigan. It contained a threat to injure the person it was addressed to, as well as another person.

Two weeks later, on Sept. 3, 2020, Zink mailed another note through USPS to the U.S. District Court at 107 Federal Building, 410 W. Michigan Ave. in Kalamazoo. The handwritten letter stated that it contained the “chemical agent… anthrax” and by the time the letter was read “it will be to late for you have already came into contact with the chemical powder,” according to the indictment.

The letter did not actually contain anthrax.