CASPER, Wyo. (AP) — Authorities say a Casper man accused of taking a person hostage at knifepoint sent a letter threatening to kill a federal judge last year.

The Casper Star-Tribune reports 37-year-old David Michael Chavis was charged with mailing threatening communications for a letter sent to Judge Scott Skavdahl in December.

According to court documents, the letter threatens to kill the judge or to blow up the federal courthouse in Casper.

Chavis was arrested in August 2016 after authorities say he held a Casper office worker hostage while attempting to obtain government documents.

In a letter submitted to the court, attorney Kerri Johnson says Chavis "has an ongoing persistent delusional belief regarding what should happen in this case and cannot rationally assist me in his defense."

Chavis has pleaded not guilty.

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Information from: Casper (Wyo.) Star-Tribune, http://www.trib.com