The clues mount in the mysterious murder of Erin Johnson. And we track down the one man who may have all the answers.

For more than a year Crime Watch Daily has been in multiple states knocking on several different doors trying to find Erron Cross.

Erron Cross is the boyfriend of a young woman named Erin Johnson killed in Mexico. That woman's family believes he knows more about her death than he's saying. Today he's got a chance to respond.

It all starts with a couple heading off on vacation -- but only one of them comes home.

The family of Erin Johnson turns to Crime Watch Daily hoping to finally find out what really happened.

Crime Watch Daily has been trying to track down Erron Cross for months, once suspected of killing his girlfriend Erin Johnson in Cabo San Lucas, Mexico.

Crime Watch Daily Special Investigator Mike Mazza has hop-scotched to four different states around the country trying to get answers. Then we got a tip that Cross was working as a chef at a restaurant in the Vail, Colorado area. Then we finally found him in Avon, Colorado.

Erin Johnson's heartbroken mother Jackie desperately wants to know why her beautiful daughter was strangled to death on a beach in Mexico. Cross was the last known person to see Erin alive.

Erin Johnson, 21, went to Cabo San Luis, Mexico for a vacation with her on-again/off-again boyfriend Erron Cross in 2001.

Erin's mother Jackie, living back in Erin's hometown near Lansing, Michigan, had her doubts about the idea at the time.

"I kind of thought it was strange that she was wanting to do this vacation with him, seemed to me in our conversation they were going different directions," Jackie said.

Her lifelong best friend Schanelle Green says the relationship seemed a bit odd at times.

"Normal boyfriends don't call you 30 times a day," said Green. "They don't make you sad. They want you to be happy and do the things that make you happy."

Jackie Johnson says that Erin was preparing to leave Cross behind and move on with her life.

"I wanted to like him, but like my daughter Erin, I felt sorry for him," said Jackie. "But there was always that hesitation, something is just not right here with him. He had a blankness in his eyes. Something wasn't right.

"I was just so happy it was going to be over, they do this last goodbye, she comes back to Michigan," said Jackie.

But Cross has other plans. He later claims he asked Erin to marry him during their Cabo vacation.

"I couldn't believe that part. Where's the ring? 'She lost it in the pool.' He wanted to make it sound like she wanted to be with him. Everything was fine," said Jackie.

Things go along smoothly for the first four days in Cabo, where the couple stays at the Fiesta Inn. Later, when Cross is interviewed by Mexican police he says that he and Erin got into a loud argument at a restaurant in town, on the night of April 28, 2001.

"They went outside, the argument continued outside. He said, 'I told Erin she always does this to me, she belittles and embarrasses me in front of people,'" said Jackie.

Erron Cross tells police that Erin Johnson walked off and got on a bus back to the hotel about 17 miles away, and that's the last her saw of her.

"I think that while she was down there, she realized who he really is -- moving on," said Jackie.

He says he stayed in town drinking and ended up sleeping on the beach. But when Jackie talks to Cross on the phone the next day, she gets a terrible feeling.

"He was crying, he said, 'Erin's missing.' To me, that doesn't make any sense," said Jackie. "'Tell me what happened. Have you gone to the police?' Well, he hadn't gone to the police. I was getting very angry with him because he kept trying to explain himself and cry. He didn't have any money, and could he get some money wired? He wanted me to wire money to him because he didn't have any money. I'm getting angrier because this is getting very serious."

All she knows for certain is that her daughter is missing, so she immediately packs her bags and heads to Ccabo to find her, joined by a private investigator hired on the spot named Mark Ford.

"I didn't know him very well," said Jackie. "I had decided I'm going to Cabo, so, I was going there with Mark to find my daughter."

When they get to Cabo, Erin is still missing, and so it seems is any accountability on the part of Erron Cross.

"He'd never gone to the police," said Jackie. "Why wouldn't you go to the police if your girlfriend is missing?"

They drive along the beach searching for her along the bus route to the Fiesta Inn. But she cannot put to rest her fears about Cross, and she's even beginning to wonder about her private investigator, Mark Ford.

"He said 'Stay in the room, get telephone calls,'" said Jackie. "I looked out the window and Mark Ford and Erron Cross were sitting at a patio table outside getting something to eat. They were kind of laughing and talking. Right then there was like a gut feeling. Like, is that how a private investigator works? Is he maybe trying to befriend him to get him to tell him something, but it still didn't feel right."

Jackie gets a phone call at the hotel desk.

"He said, 'We found your daughter. She's dead,'" said Jackie Johnson.

Erin Johnson's body was found strangled on a remote beach a few miles from her hotel.

Only a few possible clues are found near the body: a half-empty can of Modelo beer and a cigarette.

Mexican police zero-in on Erron Cross. They take him into custody at the airport as he tries to leave the country only hours after Erin's body was discovered. He is named as a suspect in her murder.

At the police station, news cameras are rolling when private investigator Mark Ford reassures a grieving Jackie Johnson, Erin's mother, that justice will be done.

But Erron Cross seems confident that it is all a big misunderstanding. Cross told Jackie that the last time he saw Erin she was getting on that bus back to the hotel after an argument.

But a different story emerges when Johnson family friend and journalist Joe Scott obtains the police interviews of witnesses.

"According to him he went one way, she got on a bus," said Scott. "What we uncovered to be the truth was he got on the bus with her."

Police reports show other witnesses on the bus, including the driver, say Erin did not get on alone.

"There is a witness, a bus driver, that confirms there was an American male on the bus drinking a Modelo beer," said Scott. "Only American tourists are allowed to drink alcohol on buses."

A can of Modelo beer: The same brand of beer listed in the police report, found on the beach next to Erin's strangled body.

"Also at the crime scene was the same brand of cigarette that Erron Cross smoked," said Scott.

"Halfway back to the Inn, she decided she wanted off the bus, she'd kind of had enough of what was going on," said Jackie. "It was just a deserted beach area, and he got off with her. Erron Cross got off with her. And I believe that at that time, she just told him the truth. 'I'm done, I don't want anything to do with you.'"

Suddenly Cross is released by Mexican police, who cite a lack of evidence, and he flies home to the United States.

"He actually flew home the day before I did," said Jackie. "I didn't know this but he actually was released from jail."

Erron Cross has gone from suspected killer to a free man in the blink of an eye. And Jackie says now she gets the cold shoulder from her private investigator, Mark Ford.

"I was flying back with Mark Ford, but he wouldn't sit with me, he found some other place to sit," said Jackie. "I was holding Erin's ashes, and when we landed in Detroit he couldn't get to his vehicle fast enough. He didn't say goodbye to me. He didn't say anything. He got his things and was gone. Which was really strange."

Mark Ford is the one who had private conversations with police when cross was arrested. We wanted to know if he could help clear the air on how Cross was released. So Andrea Isom knocked on his door where he lives outside Detroit. He briefly answered the door but refused to answer questions.

Ford later sent Crime Watch Daily a text that reads in part: "Jackie is well aware that the Mexican authorities were the only parties that uncovered any facts. They are also the only people who can answer your question about why Erron Cross is a free man."

But Mexican authorities aren't talking either. We've got no response after repeated requests for an interview.

Jackie Johnson says she tracked down and confronted Erron Cross soon after she arrived back home.

"I did talk to him. The thing is, he didn't deny it," said Jackie. "He would look at his hands and I'd say, 'Yeah, those are the hands that murdered my daughter.' He didn't say, 'No, they're not,' or object in any way. He didn't say any of that -- nothing."

Since then Cross has been known to move around a lot, keeping a low profile and working odd jobs. But Crime Watch Daily wants to ask him some questions, and after months of legwork through four states, including Alaska, California, Colorado and Nevada, we finally caught up with him in Avon, Colorado.

"Erron Cross. Did you kill Erin Johnson, Erron? Answer my question. We need to know."

"Leave me alone, please," Cross answers. "You need to leave me alone." Then he goes into a room and closes the door behind him.

And so the questions remain unanswered. Erron Cross has never been charged in Mexico or the United states with the murder of Erin Johnson.

But Jackie Johnson is confident that some day Cross is going to talk to somebody.

"He's not going to get away with that," said Jackie. "Something's going to happen. He's going to talk to somebody, he's going to slip up. I said, 'Next time I see you, it'll be in Mexico. You'll be going to jail.' That was my last thing I said to him."

The FBI tells Crime Watch Daily they are trying to find information that may bring Erin Johnson's killer to justice, but at the end of the day they can't handle the investigation because it is not in the feds' jurisdiction.

If you know anything about the murder of Erin Johnson, please submit a tip to Crime Watch Daily, or call or text our toll-free tip line at (844) 800-CRIME.

For more details of the case, visit the FBI information page about the Erin Johnson case.