Jennifer Hudson's estranged brother-in-law, William Balfour, was arrested late Monday in the slayings of the Oscar winner's mother, brother and seven-year-old nephew, according to Chicago police and the Chicago Tribune.
Formal charges have not yet been brought by the Cook County prosecutor's office, but Balfour was transferred from an Illinois state prison – where he has been held on suspicion of a parole violation – back into police custody.
He has been considered the prime suspect for weeks.
Balfour, 27, who is married but separated from Hudson's sister, Julia, was arrested in the first-degree murders of Hudson's mother Darnell Donerson, 57, brother Jason Hudson, 29, and Julia's son - his own stepson - Julian King, 7.
William Balfour, who previously served prison time for attempted murder and car hijacking, was arrested hours after the first victims were discovered.
The bodies of Donerson and Hudson were found shot to death October 24 in the family home on Chicago's South Side by Hudson's sister, Julia.
The body of King, Julia's son, was found three days later in the backseat of Jason's abandoned Chevrolet Suburban. All died from gunshot wounds.
Balfour and Julia Hudson married on December 30, 2006.
They lived together at the family home at first, but their relationship was marred by myriad fights over money and infidelities, according to family members.