William Balfour is accused of killing Hudson's mother, brother and 7-year-old nephew.
Prosecutors allege Balfour shot the family in a jealous rage because his estranged wife, Julia Hudson, was dating another man.
Jennifer Hudson is on the prosecution's witness list and may be called to testify.
The eyes of many prospective jurors grew wide when they realized they may be asked to sit in judgment on such a high profile case.
A dramatically different looking Balfour sat at the defense table Thursday. Gone is the wild hair and blank stare seen his mugshot. They have been replaced by a fresh haircut, crisp white shirt and yellow tie. He said "good morning" to the 150 prospective jurors when introduced by the judge. They replied with the same.
The task for the next few days is to winnow the field down to 12 jurors and six alternates.
"It's probably the most single important factor of a jury trial," said criminal defense attorney Sam Adam Jr.
The trial is expected to last one month. It will cover Balfour's rocky relationship with Julia Hudson. Court filings say she'll testify. "On July 31, 2008, after Julia told [Balfour] that they were going to get divorced in the morning, [he] told her again that, 'If you leave me, I'm going to kill you. You will be the last. I'll kill your family first,'" filings say.
Prosecutors claim Balfour "made these threats at least 25 times" in the months leading up to the murders of Julia Hudson's 7-year-old son, brother and mother. The killings drew national attention because of their connection to singing sensation Jennifer Hudson.
Attorney Sam Adam Junior helped R. Kelly beat back child pornography charges in an equally high profile case and says celebrity cuts both ways.
"Everybody has preconceived notions and if prosecutors don't bare it out, they may say, 'I love Jennifer,' but we expected DNA, we expected confessions, we expected all of these things that just never panned out," Adam said. "We can't do it."
The judge has already warned potential jurors to avoid media coverage of the case. He'll also quiz them about what they've already heard about the 2008 murders.
"I think the judge will admonish the jury that just because the victims were related to a famous person that should not in any way change their deliberations," said Stuart Chanen, former prosecutor.
On an average day, the criminal courts building will have six or seven jury trials under way -- most for murder. And most last just a few days.
Jennifer Hudson has indicated to the court she would like to attend. She may only be allowed to do that after she testifies.
The jury will be picked next week. Opening statements are expected April 23.