An Alaska couple who are antigovernment “sovereign citizens” face lengthy prison terms after pleading guilty Monday to charges they plotted to kill a federal judge and an IRS agent involved in a tax case against them.

Lonnie Vernon, 56, a member of Schaeffer Cox’s Alaska Peacemakers Militia, and his wife, Karen Vernon, 66, admitted conspiring to kill U.S. District Court Judge Ralph Beistline and IRS officer Janice Stowell in 2011 in retaliation for ruling the couple owed more than $165,000 in back taxes.

The Vernons admitted to buying a gun, silencer and hand grenades, and having a map to the federal judge's home.

Under a plea agreement, Lonnie Vernon will spend from 21 to 27 years in prison, and Karen Vernon will be sentenced to at least 15 years, the Anchorage Daily News reported in today’s editions. Both will be sentenced Nov. 14.

Lonnie Vernon and Cox, 28, were both convicted by a jury in June of involvement in another murder plot planned by members of the Peacemakers Militia. They both face up to life in prison when they are sentenced Sept. 14.

Despite his admission of guilt, Lonnie Vernon remained defiant, continuing to express the view, common among sovereign citizens, that the government has no control or authority over him, Reuters reported. Sovereigns generally believe they don’t have to pay taxes or obey most laws.

“If I'm accused of doing anything, I'm accused of freely exercising my First Amendment rights to the max,” Vernon told visiting Judge Robert Bryan of Tacoma, who presided over the case.

The federal judge told Vernon that he and others with similar antigovernment views are mistaken about their responsibilities to obey the law. “You can't decide, on your own, that you won't be part of what the government rules are,” Bryan said.