It's the case that captivated the city of Houston: A mother of four vanishes the day after spending Christmas with the new love of her life.

It's Christmas morning in 2013 for Jason Sanford and Melissa Sowders, both 26 years old. The Texas sweethearts are spending their first holiday together as a couple.

"She told me that she didn't usually get to spend Christmas or anything with her parents, so that was one thing she wanted to do. And so we went, we saw her parents for Christmas," said Jason Sanford.

Jason and Melissa met in grade school and had only recently reconnected.

Melissa was in the middle of a messy divorce with her soon to be ex-husband, 28-year-old Matthew Sowders. And they have four young daughters together, from 18 months to 8 years old.

"Matthew and Melissa married at a young age. They were basically teenagers," said John Jordan, assistant district attorney of Harris County, Texas. "They grew up together. Over a nine-year period they were together."

But they drifted apart as they got older. Heartbroken, Matthew filed for divorce. Melissa, the manager of a fast food restaurant, grants him full custody of their children while she gets her finances in order.

"She didn't have a job where she could support her four daughters," said Melissa's cousin Michelle Bierman. "So she left them with Matt knowing that his parents would help him until she got more stable on her feet with Jason."

"Matthew came from a good family, in that he was adopted by a very good family," said A.D.A. John Jordan.

Along with his twin sister from an orphanage in Nicaragua.

And while Melissa knows her kids are in good hands with Matthew's parents, she misses them desperately.

"She's never spent a Christmas without her babies and she wanted to see them," said Bierman.

So the day after Christmas she does just that. The plan is to meet her estranged husband and her youngest daughter at a local fast food restaurant.

"We spoke on the phone until he showed up. And as soon as he showed up, she told me, and she hung up," said Jason Sanford.

Jason is expecting a phone call from Melissa following her family visit.

"I'd been trying to call her, text her," says Jason.

He waits all day to hear from her, but gets no response. It's now after 7 p.m., almost eight hours since he's last talked to Melissa. Jason heads to the Harris County Sheriff's Office and files a missing-person report.

Melissa's family is notified that she is missing. Her aunt Belinda, traveling back to Nevada from Texas, touches down just in time to catch the frantic phone call.

"I just got home from Christmas and my elder sister told me that she was missing, and I'm like, 'What are you talking about? We just seen her. What do you mean she is missing?'" said Melissa's aunt Belinda Wood.

It doesn't take long for the media to get wind of the story, and the missing Houston woman becomes headline news.

Then a huge break in the case: less than 24 hours from the time Melissa is reported missing, the Harris County Sheriff's Department receives a bizarre 911 call. It's a woman on the line requesting to remain anonymous, claiming to be Matthew Sowders' neighbor. The caller tells dispatch she made an unexpected visit to Matthew's apartment, and when she looked inside:

"I saw someone's feet on the ground," the caller says on recorded 911 audio.

In a matter of minutes a deputy arrives on scene and questions the caller in person. The investigator records the conversation.

"I went to the door and starting knocking and he you know, he was there with his daughter and you know I was like 'Why is she crying?' and he's like 'Oh no, she's just upset.' The door was open and all I saw were two feet and they wasn't moving," the woman says. "I could tell they were female."

"The neighbor thought and said, 'Who's feet are those behind the couch?' And he said 'None of your business,' and slammed the door in their face," said Michelle Bierman.

Fearing someone's life could be in danger, deputies race to Matthew's apartment. When cops barge through the apartment door there's no body or evidence of a crime.

Still trying to piece together the caller's disturbing eyewitness account, detectives call Matthew down to the station for questioning. Anxious detectives start questioning Matthew immediately. Matthew offers up details cops never saw coming: Matthew claims he and his ex are in the middle of a love triangle, and Melissa is the sexual aggressor.

Then detectives ask Matthew how the visit ended.

Matthew tells cops their conversation lasted 30 minutes and then Melissa left.

Detectives ask Matthew about the alleged visit from his neighbor. He says she never came by the apartment or knocked.

Detectives ask Matthew if he will take a polygraph test.

"I'll be clear soon enough. We don't need a poly to do anything," Matthew says in the interrogation.

Matthew is defiant. He denies any involvement in his estranged wife's disappearance. He tells detectives to "look into that guy Jason."

It's been a full day since anyone has seen or heard from the 26-year-old Texas mother of four Melissa Sowders.

Then surveillance video surfaces. The video is from Christmas day at a local business run by Jason Sanford's godparents. Melissa and Jason are seen entering the business. There's plenty of smiles and even gift exchanges, but in less than 24 hours from the time this video is recorded, Melissa went missing.

Then deputies get a tip: a white 1995 Honda Accord matching the description of Melissa's car is spotted in the parking lot of a truck stop off Interstate 45.

It's located roughly eight miles from Matthew Sowders' apartment, the last known place she visited before vanishing.

The car was a recent purchase by Melissa and her boyfriend, Jason Sanford, a man cops know very little about. But that's about to change, when cops pull his police records. Jason Sanford's rap sheet reveals a violent past that's not so far in the past.

Just three months before his girlfriend went missing, the 26-year-old was arrested and charged with assault. Jason is asked to come down to the sheriff's office. The conversation is recorded. Detectives have discovered more than an assault record, there's a marriage license too. He's still married, but he claims he is going through a divorce.

And what about that recent assault charge?

"He was my best friend for 14 years, I found out he was sleeping with my wife and I got mad at him and we got into a little tussle in the street," Sanford tells detectives.

They ask him if he had anything to do with Melissa's disappearance or did anything to harm her.

"Not at all, not at all. Never, never. That was my angel, I loved her, I would give everything for her," Sanford says.

And he agrees to take a polygraph test.

When Melissa's best friend speaks with detectives, she paints a frightening picture of Melissa and Matthew's marriage, a relationship she says is filled with obsession.

"She would basically almost call me in tears like saying he won't leave me alone, he wants me back constantly," the woman tells detectives. "She was afraid to go over there."

And then something nightmares are made of.

"She told me one time that he tried kidnapping her from work one night," the woman tells detectives.

At this point, despite all the information coming in, detectives can't be sure who is responsible for Melissa's disappearance.

As detectives try to figure out who is telling the truth, another 911 call lights up the switchboard at the Harris County dispatch.

"I need to turn somebody in," the caller says.

This 911 caller is scared and wants to remain anonymous. But she has no problem blurting out one name: Matthew Sowders. The caller says she's a good friend of his. She's also his lover. She tells dispatch that after Melissa went missing, Matthew stopped by her place.

"He come over last night soaking wet from head to toe, truck was all muddy," she says.

"He said he blacked out and snapped and choked her to death and dumped her body in Spring Creek in a trash can," she says.

Police contact Texas EquuSearch, a volunteer search and recovery team with access to boats, divers and sonar equipment.

Investigators ask Matthew's girlfriend if she'd be willing to wear a wire and get him to confess once again. She agrees and sets up a meeting with her lover three days later. A digital voice recorder given to her by detectives records their conversation.

Matthew tells her he's confident he'll get away with murdering Melissa since cops haven't found a body. She pushes him to turn himself in. He says he'll think about it. The cops are listening to every sordid detail.

Then there's another big break in the case: Detectives receive information about an area of the creek where Matthew could have dumped Melissa's body, in an area where he likes to go fishing. Searchers focus their sonar detectors in that area of the creek.

New Year's Eve and New Year's Day comes and goes. It's now January 2, Day 7 in the search for Melissa Sowders.

Then search teams spot something below the water.

"We ended up finding Melissa's body in the creek," said Harris County Sheriff's Investigator Jason Brown. "And Melissa had been weighted down and was pretty deep in the water.

How do they know it's Melissa? The coroner's office will make the official identification, but there's one thing that cops zero-in on: It's a tattoo near her hip bone, four letters, one word -- "Matt."

The coroner officially identifies the body as Melissa Sowders.

But due to the cold winter-time water and the body being submerged for seven days, the medical examiner's office could not give an exact cause of death.

"But they ended up ruling the case what they call 'homicidal violence,' in other words someone did something to her. They just can't say exactly what," said Jason Brown. "As soon as we found Melissa's body, we were able to get the warrant for Matthew's arrest. So we knew that Matthew had an idea that this was coming."

Undercover special-operations teams are watching Matthew's house, ready to strike if Matthew tries to make a break it for it.

"We saw Matthew attempting to leave the house with his dad," said Brown.

Matthew is arrested and charged with his wife's murder. Unlike his last interview, Matthew doesn't want to talk to anyone except his lawyer.

Matthew Sowders is held on a charge of capital murder involving the murder of two people, including an unborn child. Melissa Sowders was two months pregnant at the time of her murder.

"According to some of Melissa's friends, she had pictures on her phone of the positive pregnancy test," said Jason Brown.

The baby wasn't Matthew's. Jason Sanford was the father of Melissa's baby.

"It was heartbreaking," said Jason. "I didn't want to believe it."

"We think that maybe Matthew saw some of the stuff on her phone related to the pregnancy, maybe that's what caused him to snap," said Brown.

After gathering all the evidence, prosecutors believe Matthew knew his wife was pregnant when he killed her, but they aren't sure they can prove it beyond a reasonable doubt.

They are forced to vacate the capital murder charge.

"We ended up pleaing him to the crime of murder, where we don't have to prove that he knew she was pregnant, but just that he wanted to kill her," said A.D.A. John Jordan.

Facing a mountain of incriminating evidence, Matthew pleads guilty to murder. No trial means we will never hear Matthew's side of the story. So Crime Watch Daily reached out to him.

Since Matthew Sowders was put behind bars, he hasn't talked to anyone. But on the day he was scheduled for an exclusive Crime Watch Daily interview from behind bars, he wouldn't even come out of his cell.

But whatever Matthew's story, it doesn't change the fact that Melissa is gone.

Melissa's children remain with Matthew's parents while their father serves out a 60-year sentence with the possibility of parole after 30 years.

But Melissa's family claims they got a worse sentence: Life without Melissa.