CHARLOTTE, N.C. — Sometimes it’s the DNA. Sometimes it’s looking at an old piece of evidence with a new eye. And sometimes, someone talks.

Charlotte’s cold case unit has had some big wins, but they’re working every day to solve the 3,700 unsolved rapes and murders.

Deep inside police headquarters in uptown, there are several rooms filled with boxes, which are filled with evidence from cold cases. Thousands of murders and sex assaults that have gone unsolved in Charlotte for decades -- now active once again.

“There are really a couple key components to solving a cold case. Evidence is the main one,” said Sgt. Darrel Price of the Charlotte-Mecklenburg Police Department.

Sgt. Price has been with the department for 37 years. He's currently the head of the cold case unit, a team of detectives dedicated solely to solving previously unsolvable cases.

“I think all of us would say we enjoy the puzzle,” Sgt. Price said. “What we don’t enjoy is when we think we’ve solved the puzzle but can’t probe it, which is often the case."

One case, in particular, plagues him.

“A young lady was found murdered in a bathtub. There is blood in a photo that is evidently the suspect’s. You can tell looking at it, it was in a different place but wasn’t collected because at the time of the murder DNA technology didn’t exist,” Sgt. Price said.

But that technology does exist now and is often the clincher in solving these old cases. Sgt. Price is hoping it could soon make the difference in the horrific case of the Myers Park serial rapist.

“From 1990-99, over 17 cases, wore a mask in every case, some of the kids were as young as 10, I think the oldest victim in her early 20’s," he said.

Each time, the man broke into a Myers Park house, kidnapped a young girl, then raped her. The case was never closed; the rapist was never caught. But the file is now back under the microscope.

"We can come back in with a fresh set of eyes and apply technology to these cases," said Anna, a sex assault attorney.

DNA helped solve another rape case, this one from 1979.

"He was in my home right there in the foyer and grabbed me. He had a ski mask on," the victim said.

The ski mask rapist is now serving a life sentence after terrorizing women in the UNC Charlotte area.

There was also recently a win in a notorious mass murder – five people killed on July 4, 1979, in an outlaw motorcycle gang clubhouse off of Independence Road.

The case was dubbed the July 4th massacre because so many bullets were fired. It was finally solved in 2015 when someone talked.

"That was cleared because both of suspects died and then people that knew what happened were able to come forward because they weren’t scared anymore."

No matter how cases get solved, Sgt. Price and his team are just grateful for every win.

"It's very satisfying to be able to contact victim's families and say, 'Hey, we finally got the break we were looking for,'" said Price.

If you have any information about a cold case, call the hotline at 704-336-2358.

Sign up for the 5 Things to Know Newsletter