SPEARFISH, S.D. – A Spearfish man has been sentenced to nearly six years in federal prison after pleading guilty to possessing unregistered firearm suppressors.
Cole Nygaard was sentenced to five years and 11 months in prison after pleading guilty in July to two counts of possession of an unregistered firearm.
Federal prosecutors say Nygaard was a passenger in a vehicle stopped by law enforcement in Lawrence County in January 2024. Officers discovered three firearms equipped with suppressors that lacked serial numbers and were not registered as required under federal law.
During a separate investigation in January 2026, authorities searched Nygaard’s residence after receiving information that he was manufacturing pipe bombs and had threatened to use them against people and a business. Investigators found nine improvised explosive devices, including metal pipe bombs and components that could be assembled into a destructive device.
Officials say one of the devices detonated while officers attempted to safely disable it, but no injuries were reported due to precautionary measures taken at the scene.
In addition to his prison sentence, Nygaard was ordered to serve three years of supervised release following his incarceration.
