From CBS News' Maria Gavrilovic:
(PITTSBURGH) - Moments after landing at the Pittsburgh International Airport this afternoon, the Obama campaign learned that the ATF had arrested two men in conjunction with an alleged assassination plot against the Democratic nominee. Obama arrived here for an evening rally at Mellon Arena.
Although the ATF said they shared information of the arrests with the Secret Service, the agents traveling with Obama were not aware of the plot.
Earlier today, the ATF confirmed that the two men, Daniel Cowart, 20, and Paul Schlesselman, 18, were arrested late last Wednesday. They were picked up by local authorities after they fired a bullet through window at the Beech Grove Church of Christ in Brownsville, Tenn.
CBS News has learned that the men told agents they planned a "killing spree" targeting an African-American school and that their final act of violence included assassinating Obama. Authorities say they did not have a detailed plan to target Obama.
Cowart and Schlesselman have been charged with possession of an unregistered firearm, conspiring to steal firearms and threats against a major candidate for President.
They have no known criminal record.
Obama has been under Secret Service protection since May 2007.