CHICAGO – A Chicago jury Friday convicted Oscar-winner Jennifer Hudson’s former brother-in-law of murdering her mother, brother and 7-year-old nephew in what prosecutors’ described as an act of vengeance by a jilted husband.

Hudson, who expressed her undisguised disdain for William Balfour when she took the witness stand, and who endured weeks of excruciating testimony about the October 2008 killings, was visibly overcome with emotion as the verdict was read. Hudson’s eyes filled with tears and she shook her head and bit her lip.

Afterward, she looked over at her sister, Julia Hudson, and smiled. Balfour, who faces a mandatory life prison sentence, showed no emotion.

Jurors deliberated for three days before reaching their verdict against Balfour, a 31-year-old former gang member who was the estranged husband of Hudson’s sister at the time of the triple murders.

With no surviving witnesses to the Oct. 24, 2008, slayings or fingerprints, prosecutors built a circumstantial case against Balfour by calling 83 witnesses over 11 days of testimony. Witnesses said he threatened to kill the entire family if Julia Hudson spurned him.

Balfour’s attorneys proposed an alternate theory: that someone else in the crime-ridden neighborhood on Chicago’s South Side targeted the family because of alleged crack-cocaine dealing by Jennifer Hudson’s brother, Jason Hudson. During the 30 minutes in which they called just two witnesses, however, they presented no evidence to support that theory.

Public defender Amy Thompson said she will appeal the verdict.

“It has always been our position and it still is that William Balfour is innocent of these murders,” Thompson said.

Cook County State’s Attorney Anita Alvarez reiterated to reporters what prosecutors had told jurors: that the evidence against Balfour was overwhelming.

Jurors said their deliberations were cordial and that Jennifer Hudson’s celebrity didn’t influence them. The verdict came shortly after jurors sent the judge a note saying they were split, although they did not say they were hopelessly deadlocked.

Jurors said afterward that it took some of them more time to piece everything together, and that a key was cellphone records showing Balfour was in the area when the killings happened.

Jennifer Hudson, who was in Florida at the time, attended every day of the two weeks of testimony, sobbing when photos of her relatives’ bloodied bodies were displayed to jurors during closing arguments.

Alvarez, who spoke to Hudson after the verdict, said the star was visibly relieved. She said Hudson had been determined to attend every day of the trial out of a sense of obligation to her mother.

Hudson, 30, rose to prominence as a 2004 “American Idol” finalist. But she became a bona fide star for her performance in the film adaptation of the musical “Dreamgirls,” for which she won the 2007 Academy Award for Best Supporting Actress.