PLAQUEMINE- In a rare and never-seen-before forensic interview, a 3-year-old girl told trained experts exactly who hurt her mother and what she heard.

The video was played to jury in court this week during the trial against the man accused of killing the child's mother.

That interview is a key piece of evidence in the murder trial of Robert Marks. Marks is accused of killing Lyntell Washington who was seven months pregnant with Marks' child, prosecutors said. Washington was a teacher and Marks was an assistant principal at a school in East Baton Rouge.

During the interview, a trained expert colors with the child and plays with Play-Doh as she gets very important answers to the questions she asks.

Interviewer: WHO HURT MOMMY?
Child: Mr. Robbie.

Interviewer: WHO PUT BLOOD IN THE CAR?
Child: Mr. Robbie.

Interviewer: WHAT DID YOU HEAR WHEN MOMMY GOT HURT? WITH YOUR EARS?
Child: I heard a boom!

Interviewer: DID YOU SEE MR. ROBBIE HURT MOMMY?
Child: Yes ma'am.

In the past, Marks has proclaimed he's innocent.

"For the family of the victim, I want to express my sympathy and reassure them I had nothing to do with this," Marks said.

Prosecutors disagree and said Marks' cell phone pinged in all the places he was the night Washington was murdered. They say phone data even showed Marks traveling to Iberville Parish, where Washington and her unborn child were discovered.

Marks was married at the time, dating Washington and had a third woman he was also seeing. In court, the third woman testified that Marks told her he was a medical professional.

"This guy was a doctor of deception, a master of coverups and—for Lyntell Washington—a doctor of death... and her new unborn child," Prosecutor Tony Clayton said.

Marks is a free man right now. He's allowed to come and go as he pleases during lunch breaks at the Iberville Parish courthouse.

"I've prosecuted Derrick Todd Lee, Sean Gillis and the worst serial killers in this area," Clayton said. "He ranks among them, the worst. This is a horrible case."

As this trial comes to a close, jurors are expected to see the gruesome crime scene where Washington and her unborn child were found.

Prosecutors are confident that his freedom will be short-lived.

"There was an old song that they used to play at my paw paw's juke club," Clayton said. "The song would go something like this...'please come home for Christmas or by New Year's night.' I don't think he'll be coming home by Christmas, and if the jury hasn't reached a verdict by Christmas, he won't be going home by New Year's night."

If convicted, Marks will spend the rest of his life in prison.