Mark Neiweem, 28, allegedly met with others at a Cook County forest preserve to discuss getting material to make a pipe bomb, the Chicago Sun-Times said. He was charged with "solicitation for possession of explosives or incendiary devices."
The newspaper said Neiweem was on probation for punching a police officer in the face, and was ordered held without bond for alleged probation violation. The report said the suspect had a separate $500,000 bond for the pipe-bomb case.
Neiweem was in custody at Cermak Hospital, the newspaper said. His attorney said he had severe back pain and had been vomiting, the report said.
Prosecutors said Sebastian Senakiewicz, 24, born in of Poland, claimed he could blow up a train overpass with explosives, and claimed falsely to have had a vehicle filled with explosives and weapons, the Sun-Times said.
He claimed to be hiding explosives in a hollowed-out Harry Potter book, the newspaper said, but none were found in the Chicago home where he was staying.
Senakiewicz, was arrested Thursday at his home and at the time was the fourth person to face terrorism-related charges in Chicago this week, the Chicago Tribune reported Sunday.
The three are Brian Church, 27, of Fort Lauderdale, Fla.; Jared Chase, 24, of Keene, N.H. and Brent Vincent Betterly, 24. Betterly told police he lived in Massachusetts.
Police would not confirm if there is a connection between Senakiewicz and the three men arrested one day earlier.
Senakiewicz "had been planning/conspiring with more than two other individuals in the building of explosives, including Molotov cocktails which were to be used/detonated during the NATO summit," the police report said.