An excited young woman sends her best friend a text message. She thinks the guy she's been dating is going to propose to her. But this love story has several twists and turns that no one saw coming.

The story goes from Tennessee to the scorching-hot California desert. Erin Corwin went for a romantic hike in the middle of nowhere and literally fell off the face of the Earth.

The mystery of the missing 19-year-old pregnant Marine wife: Did she get lost in the vast California desert? Did she run away from a marriage on the rocks? Or was Erin the victim of a rage-filled Romeo in a love triangle gone wrong?

Erin Corwin's journey to the Southern California desert began in a horse barn in leafy Oak Ridge, Tennessee. Erin's mother Lore says that's where Erin met the boy who would become her future husband: John Corwin.

"John and Erin met at the same barn that we had our horse," said Lore. "They met when she was maybe in fifth grade. He's a good kid, you know, we liked him."

Erin's father Bill approved wholeheartedly.

As Erin matured, she realized she was in love with John Corwin, who proposed to her after John enlisted in the U.S. Marine Corps.

John Corwin was stationed at the base in Twentynine Palms, California and he asked Erin to join him. Lore worried that her shy daughter would have difficulty adjusting to life as a Marine wife. But Erin had no problem meeting people like Aisling Malakie, who became her best friend.

Speaking to Crime Watch Daily in her first national television interview, Aisling recalls the first time she and Erin met. Erin became close with the couples in the their apartment building. But one friend stood out more than the others -- another Marine who was into horses too, Chris Lee.

"Chris was my husband's best friend," said Aisling.

Chris and Erin bonded over horses. They volunteered at a horse rescue farm in Yucca Valley.

Across the hall Erin and John were dealing with a personal tragedy: Erin suffered a miscarriage. And that strain, Aisling says, quickly put Erin in the arms of another man, the Marine upstairs, Chris Lee.

"I started noticing Chris and Erin were flirting and they would be standing close to each other with each other and Erin had pointed out that she had thought he was attractive," said Aisling. "I didn't know they were as close as they were until I came out of my bedroom and found them in my living room that Valentine's Day. I had seen them kissing on my couch. Chris was leaning over Erin and I was just kind of in disbelief. I didn't really know what to say."

Aisling said that budding affair put a chill on their friendship. And that disappointment only intensified with what should have been a happy event.

Erin told friends she was pregnant again. But whose baby was it, the husband's, or the boyfriend's?

Erin Corwin is married to one Marine, in love with another, and pregnant with one of their babies.

One brutally hot Saturday morning in June 2014, Erin Corwin kissed her Marine husband John Corwin goodbye and told him she was going out for a hike. She never came home.

John waited until the next day to report his pregnant wife missing. He asked her best friend, Aisling Malakie, if she knew anything.

"He came downstairs and knocked on my door and said 'Do you know where Erin is? She went out to Joshua Tree yesterday and she hasn't returned since," Aisling said.

Erin told husband John she was scouting out scenic vistas in Joshua Tree National Park because her mom Lore was coming to visit.

"John called me that Sunday morning and said that Erin's missing, and I'm like 'What do you mean Erin's missing?' and he said 'She went to the park to look for places for you guys to take pictures," said Lore. "My first response is she's very directionally challenged."

And shortly after Erin drove off, the Marine living upstairs was also leaving for Joshua Tree. Chris Lee told his wife he was going coyote hunting.

But Aisling says her husband wondered why Lee was loading a propane tank in the back of his Jeep?

"I believe Chris's response was he was going to blow up a mine shaft," said Aisling. "He was going to either shoot it or light it on fire. He was definitely the type that liked to build weapons and blow things up."

But Erin's story about hiking and Chris's story about coyote hunting were lies to cover up a secret rendezvous. Erin and Lee were having a love affair.

But that morning no one in the base housing saw them together. Chris Lee returned home around 4 p.m. Erin never did.

The next day her John Corwin reported her missing, and the search was on: Helicopters, the U.S. Marines and search-and-rescue dogs scoured Joshua Tree National Park during temperatures of more than 115 degrees Fahrenheit. It's 1,200 square miles of wilderness, an area slightly larger than the state of Rhode Island, filled with beauty, beasts and abandoned mineshafts, a place where someone could easily get lost. But searching is like trying to find a needle in a thousand haystacks.

Investigators found Erin's car parked in the gravel off a dirt road just outside the base. Footprints were found leading to tire tracks made by another vehicle.

Cops zero-in on John because he waited until the next day to report Erin missing. After an investigation he is cleared of any involvement. But they soon discover texts between Erin and a friend named Jessie from her hometown of Oak Ridge, Tennessee, from whom they found out Erin was going to the desert with Chris Lee.

"It kind of put up a red flag and then that's when this other deputy said 'This is more than a missing person case,'" said Lore, Erin's mother.

In those texts Erin said she thought Lee was going to propose. After all, he supposedly knew she was carrying his child.

She wrote: "Seriously I don't know why he would drag me to a very special place for a big dumb surprise."

Her friend asked if he was going to pop the question. Erin replied with lots of exclamation points: "Maybe !!!!!!"

Yet no one really knew for certain if the baby was Lee's. Either man, cops believed, could have motive to want her gone.

Aisling says Chris Lee talked about killing like it was a big joke.

"Chris said that he was going to hide a body and would snap necks," said Aisling. "He would just put the body down, cover it with a little bit of dirt and put the coyote on top and bury it, so if they ever came across it they would dig it up and think it was just someone coyote hunting.

"I don't have any other friends that talk about how they're gonna hide a body or how they're gonna kill somebody," said Aisling. "I watch crime shows but I never sit there and think that would be a good way to kill somebody or that would be a good way to get away with murder."

San Bernardino County sheriff's deputies bring Chris Lee in. Under their relentless questioning he only admits to the affair. Lee claims they hooked up after Erin told him her husband John was abusive.

There's no evidence that John ever was abusive to Erin, and he denies Lee's outrageous claim.

And Lee denies even talking to Erin the day she disappeared, or even that month, claiming they broke it off after his wife caught them. The detective doesn't believe him.

A second detective enters and they ask him about Erin's pregnancy. Lee says the baby was not his child.

Detectives ask Lee about a Google search he allegedly did just before Erin went missing: A search on how to dispose of a body.

What Lee doesn't know is that detectives have already matched the tires on Lee's Jeep to the tracks found near Erin's car. But without a body there's not enough to charge him with murder.

After non-stop searches for eight weeks, the chances of finding Erin alive were rapidly becoming slim to none.

Without a body, the mountain of circumstantial evidence investigators had against Lee wasn't enough to file a murder charge. Until they talked to one of his civilian friends who had gone to the area about a week beforehand. They had taken photos on the friend's cellphone of Lee at a mine shaft. It proved to be a virtual gold mine of evidence for investigators.

For several weeks searchers looked through every single mine shaft in the vast desert area, not knowing the condition of them. Some you could walk into, others you had to rappel to look for Erin Corwin's body.

Detectives showed the photos to mine expert Doug Billings.

"I didn't have to look at a map, I knew exactly where it was, so I was able to help direct the rescue team," Billings told local TV station KESQ.

Doug Billings and his crew started at 3 before the hot summer sun turned the desert into a furnace. The old mine is fragile and dangerous, wood frames rotting away from termites They carefully rappelled down the shaft, and at the bottom, in the darkness below the earth, a body.

"The search concluded with the discovery of Erin Corwin's body in a 140-foot mine shaft," said San Bernardino County Sheriff John McMahon.

Her body was so badly decomposed they couldn't initially determine if she was pregnant.

"It was a Saturday night going into Sunday, saying they found a female body," said Lore. "And they asked us not to tell anybody so that Chris wouldn't disappear. They assured me that they had their eye on Chris all the time."

A half-hour after Erin's body was found police arrested Chris Lee in Anchorage, Alaska. He moved there with his wife and daughter after being honorably discharged from the Marines.

Lee fought extradition but eventually gave in and returned to California to face a murder charge. He pleaded not guilty. Then later at his murder trial, a shocking reversal: Chris Lee says he did it.

He admitted killing Erin Corwin, recounting chilling details about how and why. Lee says they were just outside the mine and got into an argument. He says he came up from behind and strangled her with a homemade garrote. After five minutes of what had to be torture... He released his grip, and Erin fell to the ground. Lee says he dragged her body to the mine, pushed her in head-first, threw a propane canister down the shaft, and then tossed in a lit torch.

"One of the things that haunts me to this day is wondering what she was thinking when he wrapped that garrote around her neck when she was out there with somebody that she trusted, somebody that she thought loved her, you know, What was going through her mind?" said Lore.

"I was controlled by the anger" Lee said.

Unbelievably he claims she molested his daughter even though there is no evidence that ever happened.

"Yes, he confessed, but he couldn't even confess without bringing somebody else's character down with him," said Erin's friend Bernadette Hunt.

The jury didn't buy Lee's flimsy excuse for killing Erin and convicted him of first-degree murder. Lee received a sentence of life in prison without parole.

Erin's mom Lore says she's OK with Lee not receiving a death sentence.

"With the death penalty they're guaranteed multiple appeals and I don't want to have to go through this any more than we've already gone through," said Lore.

And now in the desert where Erin took her final breath, there's a memorial looking toward the entrance to the mine shaft where Lee callously tossed her body. Erin's murder made headlines across the country, so her family left a note for everyone visiting this memorial site asking them to sign this registry and you'll see inside there's comments from strangers to family and friends.

Christopher Lee has filed an appeal hoping to overturn his conviction or at least reduce his sentence.

Erin's family says they try not to think about him anymore -- he's not important to them. Remembering their daughter and what she stood for is the only thing they now care about.

UPDATE August 22, 2018:

The California Court of Appeal has denied the appeal of Christopher Lee, a former Twentynine Palms Marine who was convicted of first-degree murder for killing his ex-girlfriend, Erin Corwin, The Desert Trail reports.