Bismarck, ND (KEYZ) Convicted quadruple murderer 48-year-old Chad Isaak has died in prison.

Officials with the North Dakota Department of Corrections through a press release Monday morning announced that Isaak died Sunday night at Sanford Hospital in Bismarck just before 6:30 due to "self-harm."

Chad Isaak at trial in 2021 / Courtesy KXNews
Chad Isaak at trial in 2021 / Courtesy KXNews
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"On Sunday, July 31, 2022, at 5:44 PM, the North Dakota Highway Patrol was called to the North Dakota State Penitentiary, Bismarck, regarding a resident who had caused self-harm. The responding NDHP Trooper was told the inmate was taken by ambulance to Sanford Hospital where he was pronounced deceased at 6:24 pm.

The inmate was identified as Chad Isaak, 48.

The incident remains under investigation by the North Dakota Highway Patrol and the North Dakota Department of Corrections and Rehabilitation (DOCR). There is no further information available at this time."

Isaak was sentenced back in December to four life sentences without the possibility of parole for the 2019 murders of Robert Fakler, Adam Fueher, Bill Cobb and Lois Cobb at the RJR Maintenance and Management building in Mandan.

On June 30, 2021, he appealed his murder convictions to the North Dakota Supreme Court, arguing errors in his trial should prompt a reversal of his criminal convictions.