Horrific story of pregnant teacher killed by her cheating lover - with her toddler being the only eyewitness to the terrible crime - as new docuseries is set to lay bare chilling details

A new Investigation Discovery series is set to tell the stories of passion, betrayal, and tragedy.

The first episode of the network's Fatal Affairs: Lessons in Lust focuses on the clandestine relationship between Baton Rouge school teacher Lyntell Washington and assistant principal Robert Marks, and the deadly love triangle that followed. 

The illicit affair ended in a horrific murder of a pregnant Washington, with her toddler the only eyewitness.

Washington, 40, was a single mom when she started working at Brookstown Middle Magnet School in Louisiana in 2015, immediately hitting it off with Marks, who was conducting the interview with her.

The teacher, who grew up in an abusive household and married young to get her out of her strict household, had a troubled upbringing and relationship history that saw her constantly falling for men who couldn't provide for her and her daughter.

Robert Marks, pictured middle, murdered Baton Rouge school teacher Lyntell Washington in 2016

She and her ex-boyfriend, Darren Glasper, broke up when she was eight months pregnant leaving her to raise her daughter alone; and after dating broke and uneducated men she was desperate for stability - which is when she met Marks.

According to students and his colleagues, Marks was a 'really good guy,' highly educated and 'very well respected' in the town. His colleagues reported be was going through a separation from wife Kayla, but was a loving father to his two sons.

'He was one of those teachers that when you see him in the hallway he would wave at us, just make jokes, ask us if we want a popsicle,' Saleah Payne, a former student, recalled.

Jamicia Pink-Fisher, who was also an assistant principal at Brookstown, added he appeared to be interested in finding someone to share 'real love with.'

Marks and Washington began their passionate affair not long after she secured the job, with the assistant principal telling the teacher he and his wife had separated, and were going through a divorce but lived together in a two-story home, each having a floor to themselves.

'She would tell me how [Marks] would shower her with all this attention and compliments,' Washington's friend Melissa Mason recalled.

'Sometimes he would sit in the back of the classroom and watch her,' Mason recounted, adding she raised some concerns about him starting to date again before his divorce was finalized. 

'He's coming out of this marriage and he's moving into something so quickly,' Mason recalled saying to Washington, who replied that his marriage had been over for awhile.

Washington (pictured) was pregnant with Marks's child when he killed her and dumped her body in a ditch in 2016

Marks had been married to wife Kayla at the time and the couple share two sons. He had told Washington that they were getting a divorce 

Jamicia Pink-Fisher (pictured), who was also an assistant principal at Brookstown, added Marks had appeared to be interested in finding someone to share 'real love with' 

Washington's friend Melissa Mason said Marks would shower Washington with attention at school

Washington realized Marks was on a cruise with his wife and they hadn't divorced, furiously going to confront him 

A man found Washington's daughter wandering around in the carpark the morning after she went to meet Marks

'[She said] this is not fast for him,' Mason explained. 'This was him getting his sense of happiness.'

The couple continued their secret tryst, unbeknownst to their colleagues with the the relationship growing more serious, to the point that Marks was taking Washington and her three-year-old daughter on trips.

In June 2016, Washington found out she was pregnant, telling Mason that Marks was thrilled with the news.

'[Marks] expressed how much he was in love with her,' she recounted. 

However, things began to unravel over the summer while Washington was working at summer school when Mason received a frantic call from the pregnant mom saying she hadn't heard from Marks in two days.

Usually, she noted, he was extremely attentive and always responded to her. 

Washington looked up his Facebook only to find a picture of Marks and his wife on a cruise - still very much married.

Pink-Fisher said Washington and was determined to let Kayla know her husband was having an affair, and that she was pregnant with his child.

Mason received a phone call from a hysterical Washington not long after, reporting the pregnant mom went to his house - only to find he lived in a trailer and had lied about the house he lived in with his wife.

Determined to meet Marks face to face, she confronted him when he returned from his cruise - driving to meet him on June 8.

The pair met at a Walmart 20 minutes north of Baton Rouge - which was the opposite end of town to where Washington lived.

The next morning, a man in the parking lot saw a young girl walking around with a pillow and blood on her foot, not noticing any adults around.

The girl was not responding and he rang 911, also noticing there was blood in the front seat of the car she was standing near while on the phone. 

Counsellors from the Children's Advocacy Center interviewed the child, asking who hurt her mom, she constantly mentioned 'Mr. Robbie,' her name for Marks.

Police questioned Washington's friends, connecting Mr. Robbie to Marks and questioning him.

He admitted he had seen Washington the night she went missing, leading police to know they were dealing with a homicide. 

Police got their big break not long after, seeing footage on nearby security camera of a woman picking Marks up from a gas station. 

Washington's body was found in a cane field after being left in a ditch

Counsellors from the Children's Advocacy Center interviewed the child, asking who hurt her mom, she constantly mentioned 'Mr. Robbie,' her name for Marks

'I'm thinking Kayla Marks may have done something,' Mason admitted. 

'I'm thinking, "Oh my goodness the wife snapped."'

However, it wasn't Kayla who picked up Marks after Washington's disappearance - but a third woman whom he was also having an affair with - unbeknownst to either woman.

Washington's body was found three weeks later in a cane field, too decomposed to properly identify. However DNA testing showed it was Washington and the child was fathered by Marks.

During the trial, it was revealed he had searched how to murder his pregnant girlfriend, after pretending to be ecstatic over the baby news.

After shooting her with a gun and dumping her body in a ditch near a cane field, he drove her Toyota Corolla close to her apartment with Washington's daughter still in the car.

He also left his cellphone, which recorded where he traveled to that night.

At the trial, Marks was declared guilty by the jury within 30 minutes, with the testimony from Washington's daughter providing particularly compelling information. 

Marks was arrested and charged with second-degree murder, feticide and other charges and sentenced to life without parole in February 2021.

Washington's daughter, now 10, lives with her father, Darren .

ID’s New Series Fatal Affairs premieres Monday, July 22 at 9/8c on ID.