Julian King, in what he was last seen wearing, from Hudson's MySpace page
Julian King, the 7-year-old nephew of Jennifer Hudson
, died of multiple gunshot wounds and his death has been ruled a homicide, the Cook County Medical Examiner's office said Tuesday.
"We're not releasing anything else," said ME spokesman Sean Howard. "We possibly have a criminal out there and we have to maintain discretion."
King, the son of Hudson's sister, Julia, was found dead in the back seat of a white SUV vehicle on Chicago's South Side Monday. Three days earlier, the singer's mother, Darnell Donerson, and brother, Jason Hudson, were found fatally shot in their home.
King had been missing since the killings and police had sent out an Amber Alert for the boy.
William Balfour, 27, who is King's stepfather and Julia's estranged husband, remains in custody on a parole violation. Police called him a "person of interest" in the slayings of Donerson and Hudson, but he has not been charged with any crimes.
When asked if Balfour is a person of interest in King's death as well as in the slaying of his grandmother and uncle, Monique Bond, spokesman for the Chicago Police Department, told PEOPLE: "It's all one investigation."
Bond added: "Our investigation continues. He is still considered a person of interest in the investigation."