People often say you can't help who you fall in love with. Mercedes Williamson's complicated romance cost her her life.

Her 17-year-old body was just barely concealed beneath sticks and leaves. The secrets that put her there, buried much deeper.

Why did Mercedes Williamson lose her life? What twisted motives led to her death?

Just how did a murder in small-town Mississippi become a national news story and a federal crime?

Even from the beginning, who killed Mercedes Williamson was not a mystery. Why he did it? Well, that's a whole other story.

"Fun, loving, honest," said Cathy Sue Mangum, Mercedes' aunt. "She was a very strong woman. Strong-headed, you know."

And the headstrong Alabama teen's Aunt Cathy says she had big plans for her future.

"She wanted to go to California and do the famous people's hair and makeup because she could do a better job than them other people could, and she wanted to be famous for making people famous," said Cathy.

Instead, it would be infamy. And the notoriety Mercedes craved would come for all the wrong reasons.

"She never made it," Cathy tells Crime Watch Daily.

It started when Mercedes met a 27-year-old Mississippi man named Josh Vallum -- first on Facebook, and then in real life.

"From what my sister says, he was nice, he took Mercedes out, they'd have dinner, they'd go to the movies," said Mercedes' aunt Cathy Herring Mangum. "They had a relationship. Girlfriend-boyfriend relationship."

The apparently happy couple was photographed surrounded by Josh's friends at a beach party -- a night police would learn much more about in the months to follow. Not long after that photo, for reasons still not completely disclosed, Josh and Mercedes broke up, and for the next several months they were out of each other's lives.

Then, depending on whom you believe, a chance encounter on May 30, 2015.

"That day probably started like any other day for Mercedes," said Jackson County, Miss. District Attorney Tony Lawrence. "She was walking down a parkway in Dolphin Island, Josh Vallum showed up literally on the side of the road, rolled down the window and asked her to get in the car, and Mercedes got in the car with him."

It was the last time anyone would see her alive.

Two days later, and roughly seventy miles away, the George County, Mississippi Sheriff's Office gets a call from a concerned father.

"I initially took a phone call from Josh Vallum's dad on Monday, June the First, saying that he believes his son had murdered somebody and he was under the impression the body was on his property," said Captain Ben Brown, lead investigator at the sheriff's office. "When we first got there we discovered a foul odor of, you know, decomposing flesh."

And then they see it: A dirty pink flip-flop sandal resting on lifeless legs.

"We'd come across the body, which was laying face down with loose vegetation covering the body," said Capt. Brown. "From the dress appearance it was a female. But due to the trauma to the head and insect activity, we were not able to identify who it was."

It was only after the body was sent to the morgue that authorities, and soon, the rest of the country, would learn the identity.

Shortly after Mercedes Williamson was picked up by her ex-boyfriend Josh Vallum, a body is found in the field behind Josh's dad's house.

"It was a very, very horrific scene because of the fact of the mutilation to the head," said Capt. Ben Brown. "There was no facial recognition at all."

When the body goes to the morgue it is identified as a 17-year-old boy named Michael Wilkins.

Investigative reporter Margaret Baker is working for the Mississippi Sun Herald when her colleague gets the initial story.

"And they said 'All I'm saying is there was a body, but the body had a bra on,'" Baker tells Crime Watch Daily.

That is, the body of a boy wearing a bra. Margaret Baker goes back to read her colleague's story, and while looking at the comments, something else strange catches her eye.

"I noticed somebody had said 'Rest in Peace Mercedes,' and I'm saying, you know, 'Who's Mercedes?'" said Baker.

That's when she realized that Mercedes Williamson and Michael Wilkins were one and the same.

"Mercedes was transgender," said Baker. Michael Wilkins was 14 when he transitioned to Mercedes.

"With us, it went well," said Cathy. "His daddy did not accept it at all and disowned him. It hurt him."

But Mercedes' Aunt Cathy also says that she was happy with who she was.

"I asked him, I said 'Do you feel comfortable?' He said 'I feel happy.' I said 'That's all I want to hear,'" said Cathy. "That's all that matters."

How much did Mercedes' one-time boyfriend, and now suspected killer, know about any of this?

"On June the Second, after we discovered Mercedes' body, I get a phone call saying that Josh's father has brought him in, he's turned himself in," said Capt. Ben Brown. "And that's when Jonathan Carroll, who is an agent with the task force, and myself conducted the interview with Josh."

Detective: "We'll let you do all the talking. All right?"

Vallum: "I got out of prison last year. During that summer I met this person. We talked. You know, grew to like the person a lot. I didn't know, it wasn't the person I thought it was."

In the recorded interrogation, Josh goes on to say that the two hung out three or four times a week over several months, though he doesn't know if he'd call it an actual relationship.

Vallum: "We wasn't having sex. You know, there was rules and all we ever got to do was kiss. I was thinking 'All right, well, maybe, you know, she's a virgin, she's trying to hold out.'"

And Josh says that before he ever found out otherwise, Mercedes ended things completely.

Then, that fateful day months later.

Vallum: "I pulled over, rolled down the window, I was all, 'What are you doing this evening?' She said 'Nothing' -- he said 'Nothing,' and I was like, 'Well now you got plans, get in.' And I made my intentions clear. You know, I was horny and I wanted some sex."

And even though Mercedes had, according to Josh, refused that request every time before, he claims there was no argument that day.

Vallum: "Only place that I could think to go to, you know, have sex, was my dad's house. So we get there and I drive to the back of the field. We go to kissing, you know. We were kissing and I was groping and I felt something that wasn't supposed to be there."

Josh says after that he blacked out. And when he came to?

"He was standing over Mercedes with a hammer in his hand," said Capt. Ben Brown.

Vallum: "And I panicked. And I knew -- all that was going through my head at the time was, you know, 'What the f---?'"

Then, Josh claims, he ran back to his car where he found the passenger door open, blood on the interior, and other clues.

Vallum: "My thumb was bleeding. I couldn't find my knife. I know I used the Taser, because it was laying in my floorboard."

But though Josh Vallum says the specifics are all a blank, he does admit to trying to conceal his crime after.

Vallum: "I know this makes it look bad on me because I tried to cover it up. It is what it is, I can't change what I did. And if I could, Oh God! But I went home, I got a shower, I cleaned my car, I put the Taser and that hammer in the bags. Put all that in my car. I didn't want to leave nothing at dad's house. I didn't want anybody involved in what I did."

So he took the hammer but he left the body.

"He runs to the house, he has blood all over him, and his brother sees him and he tells his, brother you know, 'For the love of God, just keep your mouth shut, don't ask no questions, it's bad, it's bad, it's bad,'" said Capt. Brown.

Vallum: "I just needed him to not say anything."

Thankfully for the people who loved Mercedes, his brother did talk, which is ultimately what led sheriff's investigators to the body, and Josh.

Vallum: "I didn't hate that person. No. I liked that person, and that's the f---ing, it's f---ed up the way it turned out."

So did it all happen like Josh said it did -- a true crime of passion?

"He was trying to claim what's known as 'Transgender Panic' or 'Penis Panic,' that he is making out with what he thinks is a female and he feels a penis and he freaks out and conducts the killing," said District Attorney Tony Lawrence.

There was just one problem with that: They have testimony from her neighbor.

"That it was no doubt that Josh knew that Mercedes had male anatomy and that that was not a problem with Josh," said Capt. Brown.

In fact, police actually had multiple witnesses claiming they were certain Josh and Mercedes were having sex long before that day. One friend says she could hear them at her home months prior.

So then what is true? As it turns out, Mercedes Williamson wasn't the only one with two identities.

Vallum: "I need to make this clear to y'all: I'm affiliated. You might know that."

FBI agent: "And who are you affiliated with?"

Vallum: "Latin Kings."

It was a major revelation, Josh Vallum himself claiming to be a high-ranking member of the notorious Latin Kings street gang -- though that's about as much as he would say about it.

FBI agent: "I got a question for you. Is there anything that you may want to reveal about maybe the Latin Kings?"

Vallum: "No."

FBI agent: "Anything?"

Vallum: "No. They had nothing to do with this. It shouldn't affect them whatsoever. I'm not a traitor."

Just a confessed murderer.

"He confessed easily to the murder itself, and for someone who's murdered somebody, he was very calm, but yet he was very evasive, especially with the gang activity," said Capt. Brown

And as police were about to learn, that had everything to do with an even bigger secret buried in Josh's phone -- one that would blow his claims of any sort of crime of passion out of the water.

It is an alarming fact: Nearly 60 transgender men and women have been violently killed in the last three years. One of them is Mercedes Williamson.

And for what? According to the man who killed her, Latin Kings gang member Josh Vallum, it was because of how he found out Mercedes was born a male.

"I moved my hand trying to do the whole foreplay-type s---, move my hand down and all this," Vallum tells investigators during a recorded interrogation. "That person wasn't who I thought it was."

But multiple witnesses say that story just doesn't add up.

"Lie. There was sexual action going on in my sister's house, and he said 'Well I didn't know,'" said Mercedes' aunt Cathy Herring Mangum. "You're a lie."

And authorities had even more evidence to support that claim, some of which Josh unwittingly offered up himself.

Vallum: "I tell y'all what, help y'all, I have a phone at my house."

Josh points police to an old phone he says might have more information about Mercedes. But he forgot what else was on that phone.

"On that cellphone, I think, told us who the real Josh Vallum was," said district attorney Tony Lawrence. "There were hundreds of pictures of male-on-male sex, of penises, and I don't know how someone can claim 'Penis Panic' when they've got hundreds of pictures of penises on a cellphone they used."

So if it wasn't that, what's the real reason Mercedes had to die?

Vallum: "We have laws."

"During the investigation, law enforcement did a search warrant at one of the gang member's homes," said Tony Lawrence. "At that home we found a binder with all the bylaws and guidelines that people were to live by."

According to copies of the actual documents seized by police, the rules seem fairly straightforward: "No stealing"; "No discussing gang business with anyone outside of the gang"; all laws one might expect from any underground organization. But then there is Rule Number 21: "No member should be involved in homosexual activities."

"And that was found just a few days after Josh Vallum's arrest, and I think that was the first thing that made me suspicious that the gang may have been the motive for the killing," said Lawrence.

In fact, as part of the investigation, police did question one of Josh's fellow gang members, who gave them a photo of Josh and Mercedes at that beach party months before. Turns out it was a Latin Kings affair, and the other gang member says he was there that night.

"And he'd told us that he had asked Josh, said, 'Mercedes looks kinda like -- are you sure Mercedes is not a man? Because she has an Adam's apple,' and Josh's response to him was, 'Well, you know, she has some hormone issue so, but yeah, she's a woman, she's a female," said Capt. Ben Brown.

So it seems Josh's own gang suspected him of breaking Rule Number 21. But then, how severe could the punishment really be?

"It's not uncommon for gangs to have the 'K.O.S.' order, which is 'Kill On Sight,' when someone commits a major violation of their bylaws and rules. He killed Mercedes to protect himself," said Capt. Brown.

And that's how prosecutors saw it, too. Josh Vallum is charged with first-degree murder by deliberate design -- though in a surprise move, when Josh finally stands before a judge, it's to suddenly own up to everything.

"He pled guilty to first-degree murder," said Prosecutor Lawrence.

Vallum never testified. There was never a trial.

"Because he does not want the Latin Kings to know the real reason why he killed Mercedes," said Capt. Brown.

And yet it's all out there now. As part of Josh's plea, he admits that after being confronted by other gang members, he decided to kill Mercedes, planning how it would happen for at least two days before he picked her up. What's more, she may have figured it out just before she died.

"She got in the car and at one point she got spooked," said reporter Margaret Baker. "She said 'Josh, am I being set up?' She was already afraid."

It was one of many chilling details Josh Vallum later revealed to Mississippi Sun Herald Reporter Margaret Baker in a jailhouse interview.

"It's not my fault," Josh said in the interview. "She got in my vehicle after I told her I wanted to have sex."

Josh says after driving Mercedes over 70 miles to his dad's property, the endgame began.

"They stop and pretty quickly he pulls out the stun gun and sticks her with that, he had the knife and he started stabbing her," said Baker.

"She said 'Oh God, Josh, please no," Josh told Baker. "She was screaming."

"She's saying she really wants to live," said Baker. "You know, 'Don't do this,' and you know, 'I'm so young.' And she managed to get out of the car, the passenger side, and ran around and he chased her."

"Hit her in the head with a hammer," Josh told Baker.

"He said he beat her on the head with the claw hammer until she fell out. He beat her a couple more times with the claw hammer to make sure she was dead," said Baker.

"I wish that I could take it back. If there was one thing I could take back I wish that that would be it," Josh told Baker.

And oddly enough, that's one thing authorities actually believe.

"This is kind of a weird case because I believe that Josh and Mercedes loved each other, but he chose the gang over that love," said Tony Lawrence. "If there's no gang, there's no killing."

For pleading guilty to first-degree murder in the state of Mississippi, Josh Vallum is given a life sentence. But that still wasn't the end of the story.

During Josh's initial interrogation, he made a telling prediction.

"I mean, with this being a transsexual, it's liable to be labeled as a hate crime," Josh had said.

He was right. In addition to his life sentence in Mississippi, Josh Vallum received an additional 49 years in federal prison after being convicted under the Matthew Shepard and James Byrd Jr. Hate Crimes Prevention Act, making him the first person ever prosecuted for a specifically trans-phobic attack.

And the tragic case of Mercedes Williamson even touched hearts in Hollywood. During her emotional speech at the ESPY Awards, Caitlyn Jenner used Williamson's murder as an example of why the former Olympian decided to come forward in a hope to "do whatever I can to reshape the landscape of how trans issues are viewed, and how trans people are treated."