The probe is focusing on a half dozen detectives who worked with retired Chicago Police Cmdr. John Burge, believed to be the ringleader of the group that routinely tortured confessions out of murder suspects, the Chicago Tribune reported Wednesday.
Burge, 61, who lives in Florida, was indicted in October on federal charges of perjury and obstruction of justice.
At the time, U.S. Attorney Patrick Fitzgerald issued a warning to officers who worked for Burge and took part in the alleged brutality.
"If their lifeline is to hang on a perceived code of silence, they may be hanging on air," Fitzgerald said.
The Tribune says subpoenas served on the city indicate prosecutors are now looking at detectives linked to Burge and the South Side precincts where he worked during the 1980s.