Leroy M. Schweitzer, the leader of the anti-government Montana Freemen movement in the 1990s, died Tuesday morning in federal prison in southern Colorado.
Schweitzer was found dead in his cell at the Supermax prison.
The 73-year-old former leader of the Freemen group appears to have died of natural causes. A Federal Correctional Complex advisory announcing the death said an autopsy will be performed.
Schweitzer was serving a 22-year sentence for his convictions in a massive phony check scheme that ultimately led to an 81-day armed standoff with the FBI on a foreclosed ranch in Garfield County.
Federal agents arrested Schweitzer and his associate, Daniel Petersen, in March 1996 in an undercover sting, while his followers ultimately peacefully surrendered to agents, ending the standoff.
A federal jury in U.S. District Court in Billings convicted Schweitzer, originally of Belgrade, of 25 crimes including conspiracy, bank, mail and wire fraud, false claims to the IRS, interstate transportation of stolen property, threats against federal officials and armed robbery of news crews and other violations.
Prosecutors said the Montana Freemen, driven by a hatred of the government, conspired to issue billions of dollars in bogus checks to cheat banks and the IRS in a scheme to get something for nothing.
Schweitzer and his associates held classes instructing others in how to issue the fake checks at a cabin south of Roundup before moving their operation to a ranch west of Jordan in Garfield County.
Schweitzer had been scheduled for release on May 16, 2019.
The Associated Press contributed to this report.