Oscar-winning actress Jennifer Hudson appealed on Sunday for the public's help in finding her 7-year-old nephew, missing since the shooting deaths of her mother and brother.
City police transferred custody of the man labeled a "person of interest" in the shooting deaths to state authorities.
An alert remained in effect Sunday for young Julian King, who disappeared on Friday, the day the bodies of his grandmother, Darnell Donerson, 57, and 29-year-old uncle Jason Hudson were found in the home they all shared on the city's South Side. The deaths were ruled homicides.
The alert listed William Balfour, the estranged husband of Jennifer Hudson's sister, Julia Hudson, as a suspect in a "double homicide investigation." Julia Hudson is the missing boy's mother
Chicago police spokeswoman Monique Bond said authorities considered Balfour a "person of interest" in the case but he had not been charged.
Authorities said the search for Julian would be citywide, but on Sunday residents and officers focused their efforts "in the immediate vicinity" of the family's home in the Englewood section, said police spokesman Dan O'Brien.
Police said they did not have a motive for the killings but called the case "domestic related."
"There's a lot of forensic evidence. We have to work the evidence and try and solve this case," Bond said Sunday. "Most importantly, we want to find the child."
Bond said no weapon had been found at the Hudson home, a three-story house sandwiched by vacant lots littered with trash. On Sunday, investigators moved in and out of the home and examined the trash.
Police officers were instructed to place fliers with Julian King's picture and description in every business in the area.
Jennifer Hudson, who won an Academy Award for best supporting actress in 2007 for her role in "Dreamgirls, was in Chicago with her family during the weekend, her sister said. A publicist did not disclose her whereabouts.
In a MySpace blog entry on Sunday, Hudson said she was grateful for community support and posted a picture of her sister's son.
"Thank you all for your prayers and your calls. Please keep praying for our family and that we get Julian King back home safely," the blog entry said. "If anyone has any information about his whereabouts please contact the authorities immediately ... Once again thank you all for being there for us through this tough time."
Bond said Balfour, who had been in police custody since Friday, was transferred Sunday to the Illinois Department of Corrections "based on his active parole violation unrelated to this investigation."
Records from the corrections department show Balfour, 27, is on parole and spent nearly seven years in prison for attempted murder, vehicular hijacking and possessing a stolen vehicle.
Corrections spokeswoman Januari Smith said Balfour would likely remain in state custody until the Illinois Prisoner Review Board looked at his case. She would not say exactly where Balfour was being held.
It was unclear if Balfour had an attorney to speak for him Sunday, but his mother, Michele Balfour, has denied that he was involved the killings or in Julian's disappearance.
During a public plea Saturday for the boy's return, Julia Hudson described her son as a smart, sensitive and easygoing child.
"He's not your typical 7-year-old," she told a crowd at the family's Pleasant Gift Missionary Baptist Church on Chicago's South Side. She was joined by the boy's father, Greg King.
Hudson said she last saw her son Thursday night when they went out to dinner to celebrate her 31st birthday. Afterward, she said, she took Julian to the home she shared with her mother and brother, handed him to his grandmother and everyone went to sleep.
Julia Hudson said Saturday that she was confident her son was still alive and that she was praying for his return.
"Momma's looking for you. I'm not going to stop until you come home," she said.
The tragedy comes as Jennifer Hudson's star continues to rise. Her song "Spotlight" is No. 1 on Billboard's Hot R&B/Hip-Hop charts and her recent self-titled debut album is selling well. She was featured in this year's blockbuster "Sex and the City" movie and also stars in the hit film "The Secret Life of Bees."
Associated Press writers Sophia Tareen contributed to this report.