Day said now is the right time to tell her story.
Laura Day spoke to "20/20".
"A tragic accident happened. I tried to save him," Day told "20/20" in her first interview.
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On October 5, 2012, Day said that she picked up her stepson, Taylor Syring, from school in Corpus Christi, Texas. It was a Friday and she said that Taylor wanted to go to the beach.
"He said he wanted to have a picnic on the beach," said Day. "It was a spur of the moment decision."
Day said the two drove home to pick up bathing suits and beach towels before going to the beach.
Taylor Syring died October 5, 2012, in Corpus Christi, Texas.
Day also told investigators that the beach was busy that day so the two had gone down to a more secluded area to avoid crowds. She said she had put a lifejacket on Taylor and watched him play in the water before taking off the lifejacket because it had been giving him a rash.
"It was giving him a rash, clearly. I said, 'If you can show me that you're OK and you feel safe enough to dive under the waves and you feel comfortable, then I'll let you swim and play in the shallow water, without your lifejacket,'" said Day.
She said she turned around to head back to the beach and by the time she turned back around, Taylor was gone.
"At first, I didn't understand. I thought maybe he'd dived under the waves and he was swimming, but then I realized he didn't surface and I ran in the water to where he was and he was gone... And then I saw him floating, face down," said Day.
"I tried to get the water out of his lungs. And it just wasn't coming out. I didn't know why. I panicked. And I was disoriented. I wasn't thinking clearly," she added.
David Syring was the father of 6-year-old victim Taylor Syring.
Day told police she "panicked" and instead of calling 911 she drove the unconscious child to a hospital 12 miles away. At the hospital, Taylor was pronounced dead.
Investigators began to question Day's story. They found it suspicious that she had driven 12 miles to a hospital because she said she believed that the paramedics would take too long to arrive. Investigators later found out that a Corpus Christi fire station was less than three miles away from the beach where Day had brought Taylor. She had also told police that even though she knows CPR, she had admitted not administering CPR to Taylor.
Police arrested Day on child endangerment charges three days after Taylor's death.
At the time, Day and Taylor's father, David Syring, had been married for two months and Taylor would visit on weekends. Day had met David Syring in 2012 while Syring was still married to his ex-wife and Taylor's mother, Kelly Syring.
"I was going through a rough patch with Kelly. And Laura was very friendly. She was married, too. She would explain to me the issues that she had in her marriage. And seemed as though neither one of us were really happy with our spouse," said Syring.
Syring admitted to having an affair with Day beginning in May 2012 and said his marriage was over. Kelly Syring said the divorce was difficult for both herself and Taylor.
Kelly Syring spoke to "20/20".
"It was not easy. I was still very much in love with him. I was very angry," said Kelly Syring. "[Taylor] was heartbroken."
Only three months after the Syrings' divorce was finalized, David Syring and Day traveled to Las Vegas to get married. They both said the marriage was a bit rushed because of a morality clause in the divorce.
"In my divorce decree, Kelly had wanted it to be put in there that there was to be no overnight guests I wasn't married to around Taylor," said Syring. "We felt like we wanted to get married. Maybe not quite that soon. But I wanted Taylor to be able to be around Laura. And Laura to be around him."
Syring said he felt caught in the middle between Day and his ex-wife.
"I didn't handle things properly with the way our relationship ended, but there was issues, because it seemed like Kelly wanted to make it hard, especially for Laura," said Syring. "And Laura was afraid that, given my close bondness to Taylor, that I would eventually one day maybe go back to Kelly."
David Syring visiting his son's grave in Corpus Christi, Texas.
Day denies that she was ever jealous of Syring's relationship with his ex-wife and the fact the two shared a child together.
"No, absolutely not. As a matter of fact, David hired an attorney - we both did - to get full custody of Taylor," said Day. "I was very secure in my relationship with David at the time. I was not jealous of anybody."
Later, investigators would record phone calls between Day and Syring where Day would ask things like, "Do you love me more than you loved Kelly?"
"Despite, you know, me telling her, over and over, that I was there with her," said Syring. "She wanted it to just be us."
Day said she loved Taylor like he was her own child.
"We went everywhere together. Movies, Chuck E. Cheese; I took him to Taekwondo and we did everything. I had a bright future for him. Even talked about saving money and putting it away for college, like I did my own son," said Day, who has a son from a previous marriage.
Laura Day during her police interview with the Corpus Christi Police Department on October 5, 2012. (Corpus Christi Police Department)
Kelly Syring said that Day was emotionless the day Taylor died.
"She was standing there. Just not doing anything. Not crying. Nothing. Just standing there. As if she had the right to be there," Kelly Syring told "20/20". "All I could do was just cry. Just lay my head on my son, and just cry."
David Syring and Day were brought down to the Corpus Christi Police Department that evening for questioning.
"I just assumed that this was kind of just routine and I wanted to be able to help any way I could, just to make sure everyone had all the information that they needed," said Syring.
During the interview, Syring had told police that a week before Taylor was killed he had found out through an online search that Day had been connected to a series of crimes, including another murder. Syring said that when he had confronted Day with the information, she had told him that "it was not her."
"I took her word for it... she gave me an explanation as to these circumstances. And gave me explanations that seemed believable and plausible," said Syring. "And I believed her."
In May 1982, Day, who was 17-year-old Laura Feist at the time, was dating a 21-year-old college student named James Kendall in Laguna Beach, California. When Kendall decided to end the relationship, Day shot and killed him before turning the gun on herself, according to Jason Kravetz, a former officer with the Laguna Beach Police Department.
She had told investigators at the time that she was a victim of abuse and that she was acting in self-defense. Investigators could find no indication, however, that Kendall was ever abusive. Day pleaded guilty to second-degree murder and was sentenced to the California Youth Authority rather than prison.
Laura Day as Laura Lee Feist courtesy of the Long Beach Police Department. (Long Beach Police Department)
When ABC News questioned Day about the murder, she refused to discuss it, saying "I'm not supposed to talk about that. My attorney told me not to," said Day.
After she was released, Day changed her name and married several times. Over the years, she was accused of or convicted of theft, fraud, burglary and bigamy, according to police reports.
After Day was interviewed by the Corpus Christi police, she returned home. But soon after police recounted her timeline, she was arrested on charges of child endangerment. Syring said he thought it was a mistake at the time.
"I figured that the police may have had some questions or doubts. I couldn't see it as anything other than an accident. Especially the way she described the events," said Syring.
After Day posted bail for $50,000, she returned home in less than 24 hours. Syring said she had been acting strange.
"Laura was just trying to get back to life as usual. Trying to figure out whatever it would take to keep me happy. Talking about the possibility of us packing up and moving, and going to Florida," said Syring. "Trying to get me to get past my feelings, trying to get me back to acting normal, which seemed a little strange to me. I mean just so sudden."
A break in the case came when a witness named Rene Ruiz came forward. Ruiz said he was fishing on the beach the day Taylor died and had seen Day.
"The most upsetting, troubling, telling thing that Rene Ruiz said, is that when she ultimately left the beach - now remember, according to her, she has a dying boy in the back of her car - she waved and smiled at him, as she drove off the beach," said former prosecutor Brittany Jensen.
Prosecutors also alleged that Taylor was not the one who suggested the trip to beach. Investigators had found Taylor's clothes in Day's car, suggesting that he changed in the car and that the two never went home before the beach. Day claimed that Taylor had changed in the car because he was finishing his snack first.
They later would collect evidence from Day's jail phone calls to Syring, where she explained that she had never gone home after picking Taylor up from school.
In January 2013, Day was charged with capital murder in addition to child endangerment.
While the prosecution continued to build its case, investigators were contacted by a drowning expert who looked into the conditions of the beach on the day Taylor died.
"When Laura Day stated that Taylor Syring's body sunk, and then popped up 50 yards to the right, the problem was that was the wrong direction. Based on the conditions and the wind and everything else that day, it would've gone left and not right," said Jensen. "It is highly improbable that she would have been able to locate him quickly, unless she was right next to him. Everything was all lies."
Rene Ruiz during his police interview with the Corpus Christi Police Department. (Corpus Christi Police Department)
After six days of trial, Day was found guilty of first-degree capital murder and sentenced to life in prison without parole.
At the time, Syring was still convinced that Day was innocent and the couple hired a new attorney to handle her case.
"You can't keep your eyes on your children every minute, wherever you are. It was obviously an accident," said Appellate Attorney Angela Moore.
Moore also found a drowning prevention expert, John Fletemeyer, who refuted the prosecution's expert.
"Depending on the direction the waves are coming, the long shore drift can go in either direction and that's a common factor on most beaches," said Fletemeyer, who has conducted more than 1,000 forensic investigations into drownings, according to his website. "Certainly could explain why the little boy was 50 yards down the beach."
For now, Day is waiting to see if the Texas Court of Criminals will order her a new trial.
David Syring spoke to "20/20".
As for Syring and Day's relationship, the couple is now divorced. Syring said he believes now that Day is where she belongs.
"I believe that this is probably the worst punishment for her. To be in prison," said Syring. "She has never apologized. She has never said sorry for what she's done. I feel so stupid to have been this naive and to have stuck by her as long as I did."
Kelly Syring has lived nearly a decade without her son. She said she has forgiven what she can.
"Well, I have forgiven Laura. That doesn't mean she needs to come out of jail. Look at that, why should she get off so easy? She gets to spend the rest of her life in a jail cell. Miserable," said Kelly Syring. "And as far as my ex-husband... I blame him, too. I do blame him. This is partly his fault. He knew about her past."
Syring said he's doing what he can to move on.
"I was so wrapped up in, tangled up in all of this, that so many things, so many red flags, escaped me. I don't know if it was just, you know, the trauma of losing my son, I don't know if it was her being a great manipulator. I can't explain it," said Syring.
Day continued to write Syring until 2019, when he stopped writing her back. She did, however, find a new boyfriend through a pen-pal service in prison.
Jensen said Taylor will always live on in her memory as a reminder that justice does exist.
"To this day, I have a picture of Taylor Syring on a shelf directly across from my desk. I see him every day, while I'm working," said Jensen. "And I do that because the justice that the case team and I were able to get for him was one of the more incredible things I think I'll ever do in my career."