Chicago (CNN) -- A Chicago jury found William Balfour, Jennifer Hudson's former brother-in-law, guilty Friday on three counts of first-degree murder and four other counts related to the 2008 slayings of the entertainer's mother, brother and 7-year-old nephew.
He will be sentenced to life without parole; Illinois has no death penalty.
Hudson, who was in the courtroom with her sister Julia and fiance, David Otunga, broke down in tears as she heard the verdict. Otunga said, "Yes," and put his arm around her.
Hours later, the two Hudson sisters released a statement thanking God, the prosecution team, "the best police department" and "people all over the world" for their support.
"It is our prayer that the Lord will forgive Mr. Balfour of these heinous acts and bring his heart into repentance someday," the sisters said in the statement, which was posted to Jennifer Hudson's website and linked to via Twitter.
In addition to murder, Balfour was found guilty of aggravated kidnapping, home invasion, residential burglary and possession of a stolen vehicle.
A public defender for Balfour said his legal team would file a motion for a new trial on June 8 and then file a notice of appeal.
"I do feel there were very strong issues of law in this case that need to be looked at by an appellate court," Amy Thompson told reporters outside the courthouse. "So we do have some hope."
CNN Legal Analyst Sunny Hostin expressed surprise at the verdict. "This wasn't a slam-dunk case," she said, citing a lack of forensic evidence.
The case went to the jury Thursday, after heated closing arguments Wednesday set a tense tone.
In the middle of the afternoon on Friday, the jurors sent Judge Charles Burns notes saying they were split and asking to see testimony about cell phone records showing that Balfour's phone was near the site of the killings at the time they took place.
The split was then nine to three in favor of conviction, said juror Jacinta Gholston, who works for a Chicago-based chocolate company. "There were three of us who just needed to see the picture a little clearer," she told reporters after the verdict.
The records proved key. An hour later, jurors told the judge they had reached a verdict. "Once we got those holes filled, we were able to come to a unanimous decision," Gholston said.
Juror Paula Halcomb, a math teacher in the suburbs southwest of Chicago, also cited the cell phone records as persuasive. "We realized that he could not be in two places at one time," she said.
Hudson's testimony played no role in the jury's decision. "She didn't really say anything," Halcomb said.
Hudson, who was called as the prosecution's first of more than 80 witnesses, broke down in tears several times on the stand as she recalled her family.
"None of us wanted her to marry him," Hudson said of her sister's decision to marry Balfour. "We did not like how he treated her.
"Where he was, I tried not to be," she said.
"This wasn't a case about Jennifer Hudson," Gholston said of the entertainer, who attended the trial each day. "For us, her celebrity had nothing to do with it."
Jury foreman Robert Smith, 42, who works for Chicago Public Schools, said the decision was an easy one for him. "I was pretty much certain from the beginning," he said of Balfour's guilt. "To me, everything connected."
Asked what he would tell Hudson, he said, "Honest, I don't really have anything to say to her. But I just hope that she can kind of put this behind her and just get on with the rest of her life."
Cook County State's Attorney Anita Alvarez said the singer was "was very emotional about the verdict, as you can well imagine, and so was her sister and the rest of the family -- emotional but relieved."
Defense lawyer Thompson had argued that police had homed in on Balfour rather than conducting a full investigation.
"In their mind, this wasn't a whodunnit," she said.
No DNA evidence pointed to Balfour, said Thompson, who also questioned police work in the case, describing a set of keys that she said surfaced on an evidence list a month after the slayings.
"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.
CNN's Katherine Wojtecki contributed to this report.