An Amber Alert was issued for the boy on Friday after Hudson's mother and brother -- the boy's grandmother and uncle -- were found shot to death in the family home.
FBI Deputy Director John S. Pistole said at a news conference that authorities found a body "who we believe to be the missing victim in Chicago, the nephew of Jennifer Hudson. We are working with Chicago police to get a positive identification of the victim."
The remains were found in back seat of the white SUV being sought as part of the investigation. The vehicle was parked on the street of a residential area, approximately 14 miles from the original crime scene.
Hudson had offered a $100,000 reward on Sunday for the safe return of her nephew, the son of her sister Julia Hudson. The boy's stepfather, William Balfour, is being held on suspicion of murder in the case but has not yet been charged.
Balfour spent nearly seven years in prison for attempted murder, vehicular hijacking and possessing a stolen vehicle.
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