Police had been searching for the boy since the bodies of his grandmother Darnell Donnerson and his uncle Jason Hudson were found in their Englewood home.
No one has been charged in the case, but Superintendent Jody Weis is pleased with the investigation.
"We've still got a lot more to do," said Supt. Jody Weis, Chicago Police Department. "There's still a lot more forensic examination to do. Right now, we're extraordinarily pleased and satisfied that the weapon has been identified as the weapon that has been used in the homicides. And there's still more work to do which we are doing at this time."
The Bureau of Alcohol, Tobacco and Firearms traced gun to the original owner in Michigan who had reported it stolen. Police say William Balfour, the estranged husband of Jennifer Hudson's sister, is a person of interest in the case.
The funeral home handling arrangements for the family says there will be a public memorial on Sunday afternoon at 4 p.m. It will be held at Pleasant Gift Missionary Baptist Church at 4526 S. Greenwood.