The murder of a beloved teacher uncovers lies, an illicit affair, a secret pregnancy

In June 2016, a 3-year-old girl was found wandering alone in a parking lot in Baton Rouge, Louisiana, near a car that was splattered with blood. She wasn't wearing any shoes and her foot was speckled in dried blood.

A good Samaritan who found her kept her calm as he called 911 to get help.

"I started asking her, 'Well, where's mommy? Where's mommy's car?' And she pointed to her mom's car," Leslie Parms told "20/20." The girl's mother, who police would later learn was Lyntell Washington, a beloved teacher, was missing.

What the girl revealed would lead investigators to uncover events -- including a secret love affair -- surrounding the murder of Washington, who was pregnant when she was killed.

A special "20/20" that airs Friday, Oct. 7, at 9 p.m. ET takes a look at Washington's murder and how her daughter helped crack the case.

Washington, 40, was a single mother working at Brookstown Middle Magnet Academy in Baton Rouge. She was popular among school staff and students and was once even named Teacher of the Year at a previous school. She met Robert Marks, who was an assistant principal at Brookstown and the two began secretly dating as Marks was married at the time.

Melissa Mason, a close friend of Washington, told "20/20" that Washington told her that Marks had said that he and his wife were going through a divorce but living in the same home.

"He did say that there was this two-story house and the wife was upstairs, and he was downstairs," Mason told "20/20."

Washington would learn she was pregnant with Marks' child. A week before she went missing she revealed the news to a friend, Jamicia Pink-Fisher, who was another Brookstown assistant principal.

"Lyntell was saying, 'I'm going to let his wife know what's going on,'" Pink-Fisher told "20/20."

Washington found out that Marks was not getting divorce, and in fact was on a cruise with his wife. According to Mason, the news made Washington furious.

She sent text messages to Marks demanding he tell her the truth and also wanted to know if he was committed to supporting her and their child.

Marks and Washington met up later that night.

After Washington's daughter was found in the parking lot, detectives questioned Marks, who admitted to the affair. He said he and Washington were together the previous night and said Washington's daughter was with them.

Washington's body was found a week later in an irrigation ditch at a sugar cane field. Investigators said she was shot in the head and her body was dumped in the ditch later.

"I remember I just dropped to the floor, and then my husband caught me," Mason said. "I just couldn't process she was found dead."

As detectives continued to investigate the case, they had a big lead from Washington's daughter.

During Parms' 911 call, the girl is heard saying, "Mr. Robbie put the blood there," apparently referring to Washington's car.

"She knew who left her in the parking lot," Parms told "20/20."

The girl would repeat that "Mr. Robbie" put the blood there when an officer came to the scene.

Fisher, who came to the scene and told investigators about the affair, said "Mr. Robbie" was what the girl called Marks.

Fisher would accompany the girl to a counseling center, where she was interviewed by counselors. There, she again said that Marks put blood in the car, and revealed more details.

"You hear the little girl in her own voice saying, 'Mr. Robbie put the blood in my car. I heard a bang. My mama started shaking. My mama's asleep by a lake,'" Chuck Smith, an investigator with the East Baton Rouge District Attorney's Office, told "20/20."

Investigators would also discover that Marks was seeing a third woman, unbeknownst to his wife and Washington. Cellphone records showed Marks and Tramica Jackson exchanged several text messages and calls on the night of Washington's disappearance.

Jackson came forward to police upon seeing news reports about Washington and cooperated with investigators. She said Marks had called her the night of Washington's disappearance and asked to be picked up. The location was near the parking lot where Washington's daughter was found.

Investigators said Jackson was unaware about what had happened and had no involvement in the killing or the abandonment of Washington's daughter.

Marks was arrested and charged with second-degree murder, feticide and other charges.

During the trial, prosecutors played video of the girl's interview, where she relayed the events of the night her mother was killed. They also pointed out inconsistencies in Marks' alibi to police and offered evidence that he searched the internet for guns shortly after Washington had a sonogram that revealed the baby she was carrying was a girl.

"I told the jury, I'm going to pull up his Google records. I'm going to take his phone records. I’m going to take his computer, and I'm going put all that in a pot and I'm going cook it up," Tony Clayton, the Iberville Parish District Attorney told "20/20."

"Let's serve it to him cold like that ice cold water that runs through his veins," he said.

Marks' defense lawyer argued that the evidence was circumstantial. He didn't call any witnesses or offer a closing argument. In December 2021, a jury convicted Marks after deliberating for 30 minutes. He was sentenced to life in prison without parole two months later.

Marks' wife filed for divorce after the verdict and told "20/20" she was shocked to learn of his multiple affairs.

Washington's daughter, now 9, lives with her father Darren Glasper. Glasper told "20/20" that there are good and bad days, but he's helping her through the trauma.

"Sometimes she'd say, 'I miss mommy. I wish mommy was here,'" he told 20/20. "I said, 'I do too, but mommy's in heaven with the angels now.'"