Details are emerging from Denver on a suspected plot to assassinate U.S. Sen. and Democratic presidential nominee Barack Obama with a high-powered rifle on national TV during his acceptance speech Thursday night.

Authorities have reported a fourth arrest in the unfolding plot after the authorities in suburban Aurora, Colo., stopped a pickup truck for swerving between lanes Sunday morning in what they thought was a routine DUI.

But in the rented vehicle of Tharin Gartrell (below), a 28-year-old felon, they found two high-powered scoped rifles, ammunition, sighting scopes, radios, a cellphone, a bulletproof vest, wigs, drugs and fake IDs.

Tharin Gartrell implicated two other men - Nathan Johnson, 32, and Shawn Adolph, 33, and Johnson's girlfriend, Natasha Gromack. Nathan Johnson also reportedly confirmed the plot to FBI and Secret Service interrogators.

Shawn Adolph reportedly wore a ring with the Nazi swastika. He was injured when he jumped out of a hotel window fleeing Secret Service agents. All are now in federal custody and being detained on drug and weapons charges.

The Obama-Biden ticket will formally be nominated by the Democrats this week. U.S. Attorney Troy Eid insisted there is no credible threat to the party'snational convention or to the Illinois senator and presidential hopeful.

But a Denver television station reports that under questioning, the four men admitted there was indeed a plot to kill Barack Obama during his speech before some 70,000 supporters and a national television audience.

Story developing ...