Steven Mandell, a former Chicago police officer suspected in four plots in the past year, was placed in solitary confinement at the Chicago Metropolitan Correctional Center, the Chicago Tribune reported.
Federal prosecutors disclosed Thursday the move came after they learned Mandell allegedly tried to solicit the killing of a witness in his case in late June after he was sprung from the special unit and put into the general prison population.
Speaking in court Thursday, Mandell called the accusations "ridiculous" and accused prosecutors of "playing games."
He identified the key informant against him as Chicago Realtor George Michael and insisted Michael was in no danger from him.
Mandell also said the new accusations against him come from members of the Latin Kings street gang, whom he met while in prison.
"What I tell the other inmates ... is utter nonsense. What I say here [in court] is the truth. The Latin Kings are not fooling anyone," Mandell said.
Federal agents arrested Mandell and accomplice Gary Engel in October as they allegedly prepared to abduct a businessman from a realty office co-owned by Mandell, the newspaper said.
Prosecutors allege the businessman was to be extorted of his cash, forced to sign over real estate holdings, then killed and dismembered.
Engel hanged himself in his jail cell shortly after his arrest, authorities said.