03/13/2012 11:46 am ET

William Balfour Alibi Fake? Ex-Girlfriend Of Alleged Hudson Family Killer Called To Testify

Prosecutors say the man suspected of killing singer Jennifer Hudson's family convinced a former girlfriend to falsify his alibi, and are asking the woman to testify in the upcoming murder trial.

William Balfour, who will stand trial in April for the murders of Oscar winner Hudson's mother, brother and 7-year-old nephew, had reportedly threatened the family of his estranged wife, Hudson's sister, in the months leading up to the killings.

Now, prosecutors have called Balfour's alibi into question, claiming the alibi provided by Balfour's ex-girlfriend, Brittany Acoff-Howard, had been falsified, the Associated Press reports. Prosecutors say Balfour called Acoff-Howard immediately after the incident to request that she lie about his whereabouts.

Acoff-Howard lived on the same block as the Hudson family at the time of the murders, NBC Chicago reports.

Judge Charles Burns signed a certificate Friday confirming that Acoff-Howard failed a polygraph examination shortly after the murders last December, according to the Chicago Tribune. Prosecutors have asked the judge to name Acoff-Howard as a material witness and call her from South Carolina, where she now lives, to testify in court.

Another girlfriend of Balfour's has also been called to testify, along with Jennifer Hudson herself. Lawyers want to learn more about a phone conversation the star reportedly had with her mother on the day of the slayings.

See video from earlier proceedings in Balfour's trial: