A beloved dance instructor is shot dead as she walks into her apartment in Palm Beach, Florida in February 2003. She was talking on the phone with her best friend when she was murdered.

They say Gwendel Greenblatt had no enemies. So why was this beautiful dancer shot to death? There's motive. There's physical evidence. There's even DNA. So why is her killer still free?

Greenblatt grew up as a dancer, and that's how she moved through life, with poise and grace. She was the kind of girl who kept her chin up even in the darkest times, like when her marriage to husband, Matt Greenblatt, was falling apart.

"A few months after they got married my sister found out that Matthew was cheating on her," said Chad Piotrowski, Gwen's brother. "They separated. I think he stayed in the house, she got her own condo and they tried to work on it, or at least she did."

But she was finally letting go.

"I was going through a separation, and she said to me 'I'm going to be in the same boat as you so we'll be here together. We'll make it together,'" said Christina Vignone.

But the two friends wouldn't get the chance to go it alone.

On a warm February 2013 day in West Palm Beach, Florida, Christina Vignone would hear Gwen's cheerful voice for the last time. At approximately 3:30 p.m., as Gwen arrives home from work, Christina and Gwen chat on the phone. Then Gwen enters her apartment.

"All of the sudden she let out a scream that was not a normal scream," said Christina.

Christina then hears Gwen's phone clatter to the ground -- but chillingly, nothing else. Christina dials 911.

Authorities arrive at a gruesome scene. They find Gwen crumpled in her bedroom closet, bleeding from two gunshots to the head.

West Palm Beach Police Investigator William Fraser was at the scene.

"When she gets inside her home she's accosted, there's a disturbance in the living room, the vase is knocked over, her phone is on the floor," said Fraser.

Gwen scrambles away in terror.

"She runs into a dead end," said Fraser. "The only thing left is the bathroom and the closet. There's no place else to go."

Her pursuer raises a gun and shoots twice.

"Right through the top of her head, killing her," said Fraser.

"She wasn't just murdered, she was assassinated," Det. Fraser said.

Gwen Greenblatt dies at the hospital.

Police scour the scene for evidence. Bloodstains, Gwen's clothes, her phone. But the most shocking clue is right in plain sight.

"One of the police officers remarks, 'Look, the killer left his cigarette butt burning on the fire pull box' right next to Gwen's apartment," said Fraser. "The killer was just there. I mean it couldn't have been long if it's still smoldering."

Investigators collect the cigarette and another one stubbed out on the concrete below it.

"The cigarette was properly preserved for DNA," said Fraser.

From the start, police are very interested in talking to Gwen's estranged husband Matt Greenblatt.

Police say there's potentially a motive.

"There was a prenuptial agreement, there was a figure of approximately $70,000 that Greenblatt would have to pay Gwen if the marriage failed," said Fraser.

Police bring Matt Greenblatt in for questioning.

"Each time he talks to the detectives he gives them a different story," said Fraser.

Greenblatt claims he was getting his hair cut, returning a video, getting a pizza. But no one recalls seeing Matthew Greenblatt at all.

And the test results are in. DNA from the stubbed-out cigarette, according to detectives, is a match for Matt Greenblatt. But the smoldering butt on top of the fire alarm is not Matt's. It's someone else's.

Detectives say the physical evidence keeps mounting. Hours after the murder, police dust Matt Greenblatt's hands for gunpowder. The result: "Positive for the presence of gunshot residue."

"We said if we find the owner of the DNA on the cigarette butt, we'll solve the murder," said Fraser. "And you know what? We did find the owner. And we found it several years later and that person is Richard Engel."

Richard Engel was convicted of federal mail fraud charges. When he was arrested, his DNA is sampled, and it matches the DNA on the smoldering cigarette.

Detectives pay a visit to Engel in prison. They show him a photo lineup that includes Matt Greenblatt. He says he doesn't know any of the people in the lineup. They show Engel photos of the apartment, and tell him it's his DNA on the smoldering cigarette. Engel stammers out excuses, but detectives aren't buying them.

"I know he's lying because I have his DNA there. I don't think he's lying, I know he's lying," said Fraser.

Engel won't crack, and without linking him to Greenblatt, investigators are missing a vital connection. Engel has since been released from prison. He continues to deny his involvement. Crime Watch Daily was unable to track down Engel.

Matt Greenblatt is now a rising star in the world of sport fishing. Crime Watch Daily tried reaching Greenblatt by phone and paid several visits to his home. He declined to speak to us.

But investigators are right on his tail.

Is Matt Greenblatt a suspect in the murder of his Gwen Greenblatt?

"He certainly is," said Det. Fraser. And Richard Engel? "Absolutely," said Fraser. "I mean, why wouldn't they be? Of course they are."

While Greenblatt remains a suspect in his wife's death, prosecutors do not have enough evidence to charge him or anyone else.

Authorities are asking for the public's help in solving the case. If you have information related to the case, contact the West Palm Beach Police Dept. at (561) 822-1675.