CHICAGO (CBS) — Jurors could begin deliberating today in the case of William Balfour.

Actress Jennifer Hudson’s former brother-in-law is on trial for the murders of her mother, brother and nephew.

At the time of the murders in October 2008, Balfour was married to Jennifer Hudson’s sister, Julia.

The two were separated and she’d begun seeing another man. In its closing arguments, prosecutors tried to convince jurors that Balfour was enraged by that and carried out his repeated threats to kill her family.

Prosecutors told the jury that Balfour killed Darnell Donerson, Jason Hudson and Julian King because Julia Hudson would not reconcile with him and began seeing someone else.

Jennifer Hudson was crying during the prosecution’s presentation.

The jury is expected to begin deliberations this afternoon.

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Among the dramatic evidence the jury heard during the more than two weeks long trial: the 911 tapes of Julia Hudson after she found her mother’s body.

The defense argued that nothing directly tied Balfour to the killings and that Jason Hudson was a drug dealer with no shortage of enemies who would have wanted him dead.

CBS 2’s Dana Kozlov reports prosecutors wrapped up their case Wednesday, focusing on how authorities found a key to Jason Hudson’s SUV on Balfour after his arrest. It could be the most pivotal evidence in the case, as it’s the only physical evidence directly linking Balfour to the murders.

But defense attorneys have suggested the evidence might be tainted.

Julian’s body was found in Jason Hudson’s Chevy Suburban three days after the murders. Prosecutors have alleged Balfour stole the SUV after killing Donerson and Jason Hudson, took Julian with him, and killed the boy inside the vehicle before ditching it on the West Side.

The prosecution’s final witness, a Chicago police detective, testified one of the keys found in Balfour’s pocket after he was arrested on Oct. 24, 2008, fit the stolen SUV.

CBS 2 Legal Analyst Irv Miller said, “You always want to end big, and that’s what the state did.”

Chicago Police Det. Chester Bach testified that key was in Balfour’s pocket the day of the murders, when he was taken into custody. Bach said he personally tested every key found in Balfour’s possession, and a GM key fit the stolen SUV.

“For the prosecution, that was the key piece of evidence,” Miller said.

Other than they key, the case against Balfour has been largely circumstantial.

But, away from jurors, Balfour’s defense team raised some serious concerns about that evidence – including questions about why the key wasn’t initially listed in police reports, or inventories; and why it took three years for police to test the key.

Defense attorney Amy Thompson recalled another Chicago police detective, Thomas Kelly, who acknowledged there is no listing regarding keys in an evidence report from Balfour’s arrest.

“There’s a big hole right now. Why did they wait three years to test they key that was found in the defendant’s pocket, and the ignition of the SUV? We don’t know, and I suspect the jury may never know. It’s a burden the prosecution is going have to overcome in their closing argument,” Miller said.

Closing arguments are scheduled to start at 11 a.m. The jury is expected to get the case Wednesday afternoon.