BOISE -- An inmate at the Idaho Maximum Security Institution south of Boise will spend more time behind bars after admitting to sending threatening letters to a judge in Washington.

Brian Ray McClure, 55, was sentenced Monday to two years and eight months in federal prison. McClure is already serving time for multiple assaults on law enforcement officers but was eligible to be paroled in 2019.

According to U.S. Attorney for the District of Idaho, McClure mailed a pair of letters to King County Judge Jim Rogers on April 15, 2015, threatening to kill him and his family.

It's unclear why McClure targeted Rogers. The judge did not preside over any of McClure's cases, and the men do not have any other connection, according to prosecutors.

When a U.S. Postal Inspector interviewed McClure, he admitted to writing and mailing the threatening letters. According to a plea agreement, McClure then became belligerent and spit on the postal inspector, resulting in an additional state charge.

The federal sentence will begin as soon as McClure is paroled.