Jennifer Hudson's estranged brother-in-law has just gone from "person of interest" to prime suspect in the slayings of her mother, brother and nephew.

Chicago police today arrested William Balfour for the Oct. 24 shooting deaths that ripped the Dreamgirls star's family apart.

Chicago police detectives went to the Illinois' Stateville Correctional Center, where Balfour has been detained since two days after the murders. The 27-year-old was transferred into police custody at 2:45 local time.

“He is awaiting formal charges for three counts of murder,” a police department spokesman told E! News. “There likely will be a press conference once there are formal charges against him.”

Hudson's mother, Darnell Donerson, and 29-year-old brother, Jason Hudson, were found shot to death in the family's Chicago home. Seven-year-old Julian King, the son of Hudson's sister, Julia, was reported missing and found dead from a gunshot wound to the head three days later in an abandoned SUV.

Police said that Julian was likely taken alive from the house and then killed in the vehicle. Hudson was called upon to identify the bodies of all three.

Balfour was deemed a "person of interest" in the case almost immediately after the murders transfixed the nation. But he was jailed on an unrelated charges of parole violation stemming from a 1999 attempted-murder conviction, for which he spent seven years in prison. He was released in 2006.

At a hearing last month, the Illinois Prisoner Review Board decided to keep him locked up after hearing evidence that he appeared in places where drugs were sold and, according to his girlfriend, being in possession of a gun matching the description of the Hudson murder weapon.