Secret Service agents in Minnesota are investigating an imprisoned felon from Fargo, N.D., who they say brought a gun to a 2005 rally featuring President Bush and later made threats against the president.

David Cvijanovich began serving 19 months in jail in 2006 after a conviction for damaging government property and threatening a federal officer in 2001, reports KMSP FOX 9 in Minneapolis.

The possible assassination plot was uncovered by fellow inmates, who informed authorities. During a search of Cvijanovich's property, agents found a gun and several disguises, KMSP reports.

Cvijanovich denies the assassination attempt, saying lying convicts are just looking to get time off their sentences. He has not been charged for any activities at the rally, but is facing charges for the threats.

Click here for the report from FOX 9 News.