Nathan Johnson was arrested at a hotel in Denver.
Tharin Gartrell was arrested during a traffic stop early Sunday by police in the eastern Denver suburb of Aurora.
Authorities in Denver are investigating whether three men arrested on firearms and drug charges were involved in a possible plot to kill U.S. presidential hopeful Barack Obama during his acceptance speech at the Democratic National Convention.
Local TV station CBS4 reported early Tuesday on its website that one of as many as three people in custody told authorities that the group was "going to shoot Obama from a high vantage point" with a rifle.
FBI spokeswoman Kathy Wright confirmed the FBI was investigating reports at least one of the men had threatened Obama.
The U.S. attorney's office in Denver has scheduled a press conference on Tuesday afternoon to discuss the investigation.
But Troy Eid, the U.S. attorney for Colorado, said in a statement that authorities were "absolutely confident there is no credible threat to the candidate, the Democratic National Convention, or the people of Colorado."
The three men were arrested on Sunday following what police called an "aggressive" inquiry resulting from a traffic stop in which one of the men was taken into custody.
Aurora police Det. Marcus Dudley told reporters that officers found two rifles, one with a scope, in the vehicle, along with walkie-talkies, a bulletproof vest and driver's licences in the names of other people.
An unspecified quantity of methamphetamine was also seized during the stop, Dudley said.
Tharin Gartrell, 28, was arrested at the scene and held at an Arapahoe County jail on $50,000 bail on drug and weapons charges.
Nathan Johnson, who was arrested at a Denver hotel about three hours after the first arrest, told the CBS affiliate that others involved in the case had made racist statements regarding Obama and had discussed killing the Illinois senator on the day of his speech.
When asked if he felt there was a plot to kill Obama, Johnson said: "Looking back at it, I don't want to say yes, but I don't want to say no."
He said he wasn't involved in any plot.
About 30 minutes after Johnson's arrest, federal authorities were led to a hotel room in the Denver suburb of Glendale, where a man jumped out of a sixth-floor window to evade capture and suffered a broken ankle, Dudley said.
Shawn Robert Adolf, 33, was hospitalized and was being held on $1 million bond for several outstanding warrants involving drug charges.
The U.S. Secret Service, the FBI and a joint anti-terrorism task force have joined local police in a massive security operation during the four-day convention in Denver, where Obama is poised to become the first African-American candidate to be nominated by a major party.
And it's really sad that these sort of attempts and people talking about killing Obama are over petty things, where in comparison, Bush..... well....... he'll unfortunatly will probably live a long life in comfort.
Oh well... that's "America" for ya.