UPDATED 08/09/12 – 5:15 p.m.

JOLIET, Ill. (CBS) — Drew Peterson’s 18-year-old son, Kristopher Peterson, showed up in the courtroom on Thursday during a break in Drew’s murder trial, but Drew asked his son to leave to avoid seeing photos of his dead mother.

CBS 2’s Mike Puccinelli reports the younger Peterson had not been in court before during his father’s trial for allegedly killing Kathleen Savio, his third wife, and Kristopher’s mother. Kristopher Peterson is on both the prosecution’s and the defense team’s witness lists, so he wouldn’t have been allowed to stay anyway.

Still, for the first time in more than three years, Drew Peterson met one of his children face-to-face, when Kristopher unexpectedly showed up in the courtroom during a break in the trial.

CBS 2 sketch artist Cheryl Cook was there when the youngest of Kathleen Savio’s two sons walked in and greeted his father.

“Their eyes met. … It was a gift for him to see his son in court,” Cook said.

The two sat together in the courtroom for about five minutes. Cook said it was clear the moment was special for both father and son.

“I kind of felt like they were trying to fit a lifetime into a moment,” Cook said.

The meeting appeared to be timed, in part, to mark a milestone in Kristopher’s life.

“First words out of his mouth were ‘Happy birthday, son.’ I guess yesterday was his son’s 18th birthday,” Cook said.

But the joy of a birthday was tempered by the harsh reality that Drew Peterson is on trial for allegedly killing Kristopher’s mother. That was abundantly clear when Cook overheard Drew bring up Kathleen Savio to his son.

“He kind of warned his son that he would have to be leaving the room, because pictures of mom were about to be shown,” Cook said. “He (Kristopher) understood, nodded, and then the court officers came over to escort him out, because they knew they were about to begin.”

Kristopher Peterson came to the courthouse on Thursday, in part, to sign legal documents clearing the way for the dismissal of a wrongful death lawsuit against his dad, which had been filed on his behalf while he was still a minor.

His signature removing himself from the lawsuit essentially puts an end to the civil case.

Meantime, at Drew Peterson’s murder trial, only one witness took the stand on Thursday.

Mary Parks told the jury Savio showed her marks on her neck, and said Drew Peterson had grabbed her by the neck, and pinned her down, before saying “why don’t you just die?”

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Peterson is on trial in the alleged murder of Savio, his third wife, whose body was found in a dry bathtub in 2004. Her death was originally classified as an accidental drowning, but was reclassified as a homicide following an exhumation in 2007 after Peterson’s fifth wife, Stacy, disappeared.

Parks, a nursing school classmate of Savio’s at Joliet Junior College, testified Savio confided in her in a lab on one occasion in the fall of 2003.

At the time, Parks testified, Savio looked like she was in shock. She was wearing a long-sleeved fleece top with a high collar, which was zipped with the collar up. Savio unzipped the top to display three marks on her neck – on either side and in the middle, Parks testified.

“(Savio) told me that the evening before she was coming down the stairs and her husband came in the house and he grabbed her by the neck and pinned her down,” Parks said.

She continued: “Kathy told me she said that her husband said that her husband at that point said to her, ‘why don’t you just die?’ I told her she should call the police. I offered for her and her sons to come live in my home. She did not.”

Jurors were instructed to consider Parks’ testimony for intent and motive.

It was the second instance of hearsay testimony that jurors have been allowed to hear during the trial. Such testimony is normally barred in criminal trials, but a law prompted by the Peterson case opened the door for several hearsay statements in the Savio murder case.

On Wednesday, Will County Judge Edward Burmila agreed to allow previously barred testimony that Peterson allegedly threatened to kill Kathleen Savio and made it look like an accident.

The previous judge in the case, Stephen White, had barred prosecutors from allowing Savio’s friend, Kristin Anderson, to testify that Savio told her Peterson said, “I could kill you and make it look like an accident.”

Anderson, who lived in Savio’s home for a couple months in 2003, first testified about that alleged incident at a hearing in 2010. Prosecutors said Anderson would also testify Savio told her Peterson broke into her home dressed in black and threatened her.

The defense said Judge White found the statements to be unreliable, but Burmila said he is not bound at all by White’s rulings on what hearsay statements can be presented to jurors, opening the door for more than a dozen other previously-barred statements to be used at trial.