It's called 'hearsay evidence,' and under a new Illinois it can be allowed in some murder trials.
At the end of the hearing, which could last two to three weeks, the judge is going to decide if the hearsay evidence will be allowed into the trial.
If the judge does allow it, it will mean a lot for the prosecution. During this hearing, the prosecution is going to present 50 to 60 percent of their case.
In the case against Drew Peterson, Will County State's Attorney James Glasgow is going to present is hoping, if not counting, on new state law that allows victims to speak from the grave.
In this case, the victim is Savio, who was found dead in a bathtub six years ago.
It's up to the judge to decide if statements Savio said or wrote to others about threats Peterson made will be allowed in the trial.
"If they don't get any of the hearsay in, their case is gone. Also, from a strategic standpoint, we have a good look at what the state's case is going to be," said Peterson's attorney, Joel Brodsky.
The state called a former co-worker of Savio to the stand. Issam Karam testified that Savio told him that one night, Peterson broke into her home and "tackled her, threw her on the stairs, put a knife to her throat, and said he would kill her right there but couldn't because it would be too bloody."
The testimony did not come as a surprise to the spokesperson for the family of Peterson's fourth wife, Stacy, who disappeared more than one year ago.
"What we know of the two women, what we had heard, and what we know of Stacy and what she had told us, it all comes together," Pam Bosco said.
The hearsay evidence also includes statements Drew Peterson made to others. His former Bolingbrook police partner, James Coughlin, testified that in February 2004, he ran into Peterson at the Will County courthouse, following a court proceeding between Peterson and Savio. Coughlin testified that Peterson told him, "She got all my money. Life would be easier if she were dead."
Stacy Peterson's uncle, Kyle Toutges, told the judge that he remembered a conversation with Peterson two weeks after Savio's death. Toutges said Peterson's friend implied that he might have had something to do with Savio's death. Toutges said Peterson responded by saying, "Let them prove it."
"It's not right. That was somebody you lived with, somebody you loved.
Prosecutors say their case would be a lot easier if the hearsay evidence is allowed in. During the rest of the hearing, prosecutors are expected to be calling dozens of witnesses.