"Those keys show how desperate the state was. They resorted to this. ... My client is an innocent man," she said.
But prosecutors argued that physical and circumstantial evidence linked Balfour to the killings and described as "absurd" defense claims that police may have planted evidence or been part of a conspiracy to frame Balfour.
Prosecutor Jim McKay told jurors that there was a "tsunami of circumstantial evidence."
"The circumstantial facts of this case are drowning this guy in guilt," he said.
Cook County prosecutor Jennifer Bagby said in her closing argument that Balfour had threatened to kill the family of Julia Hudson.
"If you leave me, I'll kill you. I'll kill your family first. You'll be the last to die," he had said, according to Bagby.
"He went in that house for one reason, and one reason only, to carry out that threat," Bagby told jurors.
Balfour was accused of fatally shooting Hudson's mother, Darnell Donerson, 57, and the singer's brother, Jason Hudson, 29, in their Chicago home in October 2008. The body of Hudson's nephew, Julian King, was found three days later in an abandoned vehicle.
Prosecutors portrayed Balfour as a jealous man who murdered the three in a rage at the thought that his wife had a boyfriend.
In her closing argument, Bagby said Balfour shot Hudson's mother as she tried to defend herself with a broom.
"He fired that gun at her over and over and over," Bagby said.
McKay called Balfour "a true coward."
"He shoots a 57-year-old grandmother in the back. He shoots a 29-year-old man in his sleep. He shoots a 7-year-old twice in the head," McKay told jurors. "The family, the community, the city, the country demand justice."
In the trial, 83 witnesses testified over 11 days.
The crimes took place a year after Hudson, who rose to fame as a contestant on "American Idol," won an Oscar for her role in the movie "Dreamgirls."
In a recent interview with CNN's Piers Morgan, Hudson reflected on the life of her mother.
"My mother was a very wise and strong person. I feel like she raised us well, and she prepared me well, and so that's what I live by," she said.
Her career has continued to blossom and remains varied since her relatives' deaths.
Recent milestones include penning a memoir detailing her struggles with her weight; being cast as Nelson Mandela's ex-wife, Winnie, in an upcoming movie; releasing a new album; and singing a well-received tribute to Whitney Houston at the Grammy Awards in February.