A Chicago man pleaded not guilty today to charges that he threatened to blow up a train overpass during the NATO summit in May.

Sebastian Senakiewicz, 24, entered his plea before Cook County Criminal Courts Judge Nicholas Ford. He is being held on a $750,000 bond on charges of falsely making a terrorist threat.

Prosecutors allege that Senakiewicz, a purported member of the anarchist group "Black Bloc," boasted he had a carload of explosives and that he was determined to use them during the May summit. He also allegedly told associates he had two homemade explosives in his home, hidden in a hollowed-out Harry Potter book.

But a police search turned up no bombs, authorities said.

Senakiewicz, a Polish native who worked as a mechanic and is known by the nickname Sabi, was arrested at his home in the 3600 block of North Odell Avenue a few days before the NATO summit began.

Senakiewicz’s case was not directly connected to the so-called “NATO 3” defendants, who were charged with conspiring to firebomb political targets during the summit, or to a fifth defendant, Mark Neiweem, who was charged with attempting plotting to build a pipe bomb. But defense attorneys have said they believed the same two undercover officers or informants had infiltrated protest groups and were responsible for all five arrests.

His lawyer, Melinda Power, also said last month that any statements Senakiewicz made appeared to be just drunken bluster.

jmeisner@tribune.com