- See a slideshow of the Democratic National Convention
- Click here for John North's Blog from the 2008 Democratic National Convention.
Inside Gartrell's truck, police say they found bulletproof vests, two rifles -- including one with a scope -- ammunition, walkie-talkies and drugs.
"The ammunition, the weapons -- clearly that would give one great concern. So, as a result to that, we did the right thing," said Detective Marcus Dudley, Aurora Police Department.
At a news conference in Aurora on Monday, a police spokesperson said Gartrell led investigators to two other suspects. Nathan Johnson, 32, was arrested at about 4:30 a.m. Sunday at a Denver hotel. Shawn Robert Adolf, 33, was arrested at an Aurora hotel after allegedly trying to escape officers by jumping from a sixth-floor window. Adolf was sent to the hospital and is being held on $1 million bond.
ABC News learned that a witness interviewed in this case said one of the suspects told the witness the guns were to be used to kill Obama, who is to appear at the Democratic National Convention.
Federal and local authorities are trying to figure out if there was an actual plot with the means to carry it out, or if it was just all talk.
"Clearly we feel that there are federal implications. Otherwise, we would not have notified those agencies. Beyond that, I cannot elaborate because, again, the investigation is ongoing at the federal level," said Detective Dudley.
Officials with the FBI; the Secret Service; the Bureau of Alcohol, Tobacco, Firearms and Explosives; and Aurora police say they will reveal more details on this investigation on Tuesday.