Chicago prosecutors say they want to call as a material witness the ex-girlfriend of the man accused of killing Jennifer Hudson's mother, brother and nephew.

William Balfour, the 30-year-old estranged husband of Jennifer's sister Julia, has been charged with the 2008 slayings. His trial is to begin next month.

The Chicago Tribune said Balfour's 21-year-old former girlfriend, Brittany Acoff-Howard, may be called to testify he asked her to lie about his whereabouts the day the three people were shot to death.

At the request of prosecutors, Judge Charles Burns signed a certificate naming Acoff-Howard as a material witness. The document is being sent to the woman in Berkeley County, S.C., where she now lives, the Tribune said.

Acoff-Howard was a neighbor of the Hudson family at the time of the killings, the newspaper said.

Jennifer Hudson is a Grammy Award-winning singer who won an Oscar for her role in the movie musical "Dreamgirls."