Body believed to be Jennifer Hudson's nephew

William Balfour, 27, was also charged with one count of home invasion, authorities said at a news conference.

Balfour is the estranged husband of Jennifer Hudson's sister, Julia Hudson, and the stepfather of one of the victims, 7-year-old Julian King.

The motive for the shootings was "domestic-related, between him and his former wife, and that's about as far as we can go," said Deputy Police Superintendent Steve Peterson.

Balfour was first detained for questioning on October 24, the day Hudson's mother, Darnell Donerson, and brother, Jason Hudson, were found shot to death in their home on Chicago's South Side. Authorities said at the time that they were holding Balfour for an unspecified parole violation.

The child's body was found three days later in an abandoned SUV on the city's West Side. Authorities later found a handgun near the vehicle. Peterson said Wednesday that gun was linked to the shootings, and police believe the boy was killed in the SUV.

Balfour "has made statements about the investigation," Peterson said. "However, at this time, we don't want to go into what was said."

Police Superintendent Jody Weis said Hudson's family was "a key partner in this investigation, cooperating with detectives every step of the way under very stressful and painful circumstances." Members of the community also assisted in various ways, he said.

The family is "relieved and happy that the Chicago Police Department was able to bring this case to a successful conclusion," Peterson said.

Hudson's publicist refused to comment, citing the ongoing investigation.

Balfour was served with a warrant Monday afternoon at the Statesville, Illinois, prison where he was being held for violating his parole, Weis said. He was released from the prison into the custody of Chicago police, authorities said, and was being held in a district jail pending a hearing set for Wednesday.

Authorities said Tuesday that Balfour's girlfriend was cooperative in the investigation, but did not elaborate.

According to the Illinois Department of Corrections, Balfour spent nearly seven years in prison for attempted murder, vehicular hijacking and possessing a stolen vehicle. He was free on parole at the time of the shootings.

Hudson won a best supporting actress Oscar for her portrayal of Effie in the film version of the Broadway musical "Dreamgirls." She competed on the third season of the singing competition "American Idol" in 2004, becoming one of the top seven contestants before being eliminated from the contest.

Michele Davis-Balfour, Balfour's mother, passionately defended her son Monday to a gaggle of reporters. She said that at least one of the witnesses that police used to build a case against Balfour was lying.

"My son did not do this. I am sick of this. They need to focus on somebody else," Davis-Balfour said.

She said Balfour has an alibi -- he was with one of his three girlfriends the night of the slaying.

"He was with Diana that night and with Kate in the morning," she said.

Balfour's attorney, Josh Kutnick, also said Balfour has told him that he did not commit the crimes.

"He believes when the evidence comes out, he will be found not guilty," Kutnick said.

Balfour had a parole hearing scheduled for later this week, but Peterson said Wednesday that the approaching hearing did not influence the timing of the charges being filed.

Regarding the strength of the case against Balfour, Weis said, "You never know how a jury is going to decide cases ... but I am confident that the evidence that's been collected, the testimony that's been secured is strong, and I think we can make a very viable case in court."