Nathan Johnson pleaded guilty Tuesday in Denver federal court to possession of a firearm by a prohibited person. He faces up to 3 years, 1 month in prison at his March 20 sentencing.

Johnson and two others were arrested in Aurora on Aug. 24, the day before the convention began. Authorities said they had methamphetamine, bulletproof vests and guns with them when arrested.

Witnesses said the three had discussed killing Obama because he's black. But prosecutors determined they posed no credible threat and did not charge them with making threats.