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By Tim Stelloh

A 22-year-old Ohio man pleaded guilty Monday to planning an attack the U.S. Capitol during last year’s State of Union, authorities said.

In a plea agreement, Christopher Cornell admitted that the plot was aimed at killing government employees and was an attempt to provide “material support and resources” to ISIS, federal authorities said in a statement.

Christopher Lee Cornell, 20, of Green Township, near Cincinnati, was arrested after he bought two M-15 semi-automatic rifles and about 600 rounds of ammunition and accused of planning to attack the U.S. Capitol.Butler County Sheriff

The statement added that Cornell, of Green Township, near Cincinnati, searched online for weapons, bomb building methods and other possible targets in Washington D.C.

Cornell was arrested on Jan. 14, 2015, after purchasing two M-15 semi-automatic rifles and roughly 600 rounds of ammunition while an undercover informant watched.

Cornell initially pleaded not guilty. His father, John, told NBC News last year that he believed his son had been coerced by an informant who court records said was seeking lenience in a separate case.

The elder Cornell described his son as a quiet and shy teen who was considering becoming a nurse. But he was also directionless, vulnerable and therefore ripe for coercion, John Cornell said.

Cornell faces a maximum of 40 years in prison, the statement said.