William Balfour was formally charged with three counts of first degree murder over the shooting deaths of Hudson's nephew Julian King, seven, her mother and her brother.

The bodies of Darnell Hudson Donerson and Jason Hudson were discovered in their Chicago home on October 24 before the child's body was found in a sport utility vehicle three days later. All three had been shot to death.

Cook County state's attorney's office spokeswoman Tandra Simonton said prosecutors have handed down formal charges.

Balfour, who served seven years for a 1999 attempted murder and vehicular hijacking conviction, has been in custody on a parole violation since the first two bodies were discovered in October.

After 48 hours he was taken to Stateville Correctional Centre on a parole violation.

Police, who until this week had only said he was a "person of interest" in the case, formally arrested him on a warrant in the deaths before he was charged.

Joshua Kutnick, a lawyer representing Balfour, 27, said his client was innocent.

Balfour, Julian's stepfather, is the estranged husband of the Oscar-winning actress's older sister, Julia Hudson.

Hudson was a finalist in the 2004 season of the TV singing competition American Idol and won her Oscar in 2007 for her film debut, a supporting role in Dreamgirls.