Sheley is suspected of killing six people in Illinois and two in the St. Louis area.
The grand jury indicted Sheley's brother Joshua Sheley, Joshua's girlfriend and another man in connection with the killings.
Illinois Attorney General Lisa Madigan and Whiteside County State's Attorney Gary Spencer announced the indictments Wednesday in a joint statement but did not say what the three defendants are accused of doing.
Nicholas Sheley is suspected of bludgeoning eight people to death in late June before being captured outside a bar in the Metro East.
He has been charged with murder in four of the deaths, and authorities say he is a suspect in the others, although charges have not yet been filed.
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