There are some crime cases that are hard to forget — and then there are the cases that never go away.

In a documentary for Atlantic Voice, CBC's Yvonne Colbert spoke with three former police officers about the unsolved murders that keep them up at night.

'She got in my heart'

Retired RCMP officer Murray Brown worked with the force for 38 years. Now he has several dogs to help with post-traumatic stress disorder after decades of witnessing horrors on the job.

One case in particular has never left him.

Brown says there's rarely a day that goes by that he doesn't think of Judy Parks. The 14-year-old went missing in 1976. Her decomposing body was found three months discarded on a side road of Highway 103, west of downtown Halifax.

"There are more people than the murderer that know what happened to Kevin Martin. How it happened and how his body ended up out in the middle of no where. - Retired Stellarton police officer Hugh Muir

"She was everything a 14-year-old girl should be. She was adventurous, and she was happy-go-lucky. She was beautiful," he said.

The file was assigned to Brown after her body was found.

For years, Brown kept Parks's photo in his wallet alongside pictures of his own five daughters. He says he still avoids Halifax's St. Margaret's Road, where she's believed to have been abducted.

"It's only since I received some treatment, professional treatment, that I've been on that road, and even then maybe six or seven times," he said.

One of Brown's wishes remains punishing those that were responsible for Parks's death. He still wonders what she would be doing today if she were still alive.

"I do believe that we know who did it and from that regard, there's no real satisfaction for me," he said. "She got in my heart."

'No doubt' people know

Hugh Muir was working as a corporal with the Stellarton Police Force in Nova Scotia's North Shore region in the spring of 1994 when what appeared to be an ordinary missing-persons case came across his desk.

Kevin Martin was just shy of his 14th birthday when he was reported missing. He was part of Muir's son's class.

Muir says he never could accept that the young boy just disappeared.

For months, police received information about possible sightings, but many of the tips turned up false.

All the while, Muir spent hours driving around with Martin's grandmother, Joan, scouring places popular with kids in hopes of finding any information.

It wasn't until six years later that Martin's body was found in a shallow grave in Colchester County.

Hugh Muir says he's confident he knows who killed Kevin Martin, and that others do too. (N.S. Department of Justice, Yvonne Colbert/CBC)

Muir says not long after Martin's funeral, the boy's grandmother died — before finding out what happened to her grandson.

He's vowed the same thing won't happen to him.

Now, more than two decades later, Muir still remembers the teenager's birthday and the day he died.

Muir says he also believes he knows who killed Kevin Martin, even though charges were never laid.

"There are more people than the murderer that know what happened to Kevin Martin, how it happened and how his body ended up out in the middle of nowhere," he said. "There's no doubt in my mind that somebody does."

Just a kid, walking through a park

Tom Martin used to be one of the most experienced investigators on the Halifax police force. Now working with a private investigation company, he still struggles with unsolved murders.

"It's too tragic. It's too barbaric. We cannot just turn our backs and walk away. We have to care," he says.

Martin spent years working on homicides, including one of the province's most notorious missing-persons cases — that of Kimberly McAndrew, a 19-year-old Dalhousie student who disappeared in 1989.

There's another case he can't let go of either. Martin says he still thinks of Jason McCullough nearly every day. The 19-year-old was shot when he was walking home from a party in Dartmouth.

Tom Martin says investigators got 'very close' to finding out what happened to Jason McCullough. (N.S. Department of Justice, Martin Investigations)

Martin says both McAndrew and McCullough are what he considers "true victims" — people who didn't live high-risk lifestyles, who weren't involved with crime. "Their life taken away from them simply because they're in the wrong place at the wrong time."

He also remembers standing at the crime scene as the sun rose, just a few blocks from McCullough's home. He said it could have happened anywhere.

"One of the things about Jason's case that sticks out to me is he was roughly my son's age when it happened. Here's a kid walking through a park. It could've been any one of our kids."

Martin says investigators got "very close" to finding out what happened to McCullough.

"I believe had that work continued ... that case could be before the courts," he said.

He says his old police force should put more resources into solving homicides, including cold cases.

Reluctant witnesses

All three officers say they're concerned about what they say is the growing reluctance of witnesses to share what they might have seen.

Martin says in the early 1990s, many groups started using the phrase "the tap don't leak" and the problem has only gotten worse.

As for why people remain silent, "I can't think of a bigger motivator than fear," he said.

Despite this, Martin hasn't given up hope cold cases like that of Jason McCullough can still be put to rest.

"Justice must be served, and it's not being served. And I think that speaks volumes about us as a community and as a society."

The Nova Scotia Department of Justice continues to offer a reward of up to $150,000 for information leading to the arrest and conviction of those responsible for the deaths of Judy Parks, Kevin Martin, Kimberly McAndrew and Jason McCullough.

Anyone with information can call toll free 1-888-710-9090.