A Salcha couple has admitted to buying a gun, silencer and hand grenades, and having maps to a federal judge's homes, in what prosecutors say was a murder plot that developed from a dispute over paying taxes.

Lonnie and Karen Vernon appeared in U.S. District Court in Anchorage on Monday to change their pleas and admit to conspiring to murder federal officials. Under the signed plea agreements, Lonnie Vernon will spend from 21 to 27 years in prison.

Karen Vernon's attorney, Darrel Gardner, says sentencing guidelines call for a sentence of more than 15 years but that he can argue for less time.

In the courtroom, Lonnie Vernon constantly questioned the authority of the court to convict or sentence him and his wife.

The judge set sentencing for Nov. 14.

Lonnie Vernon was a foot soldier in a Fairbanks militia group and convicted earlier this year in a separate murder conspiracy plot in the Schaeffer Cox trial. His sentence will take care of both convictions.

Editor's note: An AP correction regarding the length of Karen Vernon's sentence has been added to this story.

Channel 2's Jason Lamb contributed to this report.