For 11 years, police thought Chrissy had run away from home. Then came an unexpected phone call.

There are some bonds that can't be broken. The connection between a mother and her child is perhaps the strongest of all, capable of spanning decades, and persisting through the darkest of circumstances.

For Mary Ann Harron, her determination to find justice for her daughter Chrissy has been a 30-year testament to a mother's undying love.

In 1993, 15-year-old Chrissy Harron was, by all accounts, a typical Canadian teenager. She didn't love school and had a history of skipping classes.

Listen to Chrissie's story on True Crime Conversations. Post continues below.

"She was messy, a bit of a tomboy and, according to a friend, a bit of an easy target for bullies," as described on Mamamia's True Crime Conversations podcast.

Behind her rebellious exterior was a sensitive girl who, as documentarian David Ridgen would later discover, had "a kind of counter-intuitive nature, that maybe she didn't get along with everybody, but she was very kind."

David Ridgen worked alongside Chrissy's mother for over 15 years as they brought her killer to justice.

On May 18, 1993, Mary Ann and Chrissy had an argument about school attendance. Concerned about the truancy officer, Mary Ann insisted her daughter go to class.

Reluctantly, Chrissy left home. That argument would be the last time she would ever speak to her daughter.

"I think that by trying to get Chrissy to go to school, she was less likely to want to go but, eventually, I think maybe a plan formulated in Chrissy's head, 'Okay, I'll go to school, but not go to school, I'll go to school the long way'," Ridgen, host of Someone Knows Something podcast, told Mamamia.

But Chrissy never made it to school that day. When she didn't return home, Mary Ann frantically called her friends, none of whom had seen her. She reported her daughter missing to the police that night, but was met with dismissive reassurance that Chrissy was just a runaway who would eventually come home.

"Well, initially, police suggest that she'll come back. You know, it's a 'she's a runaway'. And usually that's a pretty temporary manoeuvre by police. Usually it's 'give it some time'," Ridgen explained on the podcast. The local police chief even used anecdotes about his own daughter to reassure Mary Ann, saying "my daughter always comes back."

"They never found any trace of her," Ridgen said. "But if they had taken it a little bit more seriously... they could have probably found her if they did a proper search."

It wasn't until 1999, six years after Chrissy's disappearance, that the Ontario Provincial Police (OPP) took over the case. Even then, Chrissy's family was given very little information about the investigation; a common practice to protect the integrity of the case, but devastating for a mother desperate for answers.

Then came the breakthrough no one expected.

In August 2004, eleven years after Chrissy vanished, 35-year-old Anthony Edward Ringel, after having some drinks at a family party, called the police but hung up.

When the police responded, he approached the officer with his hands extended as if asking to be handcuffed, confessing, "I killed Chrissy." He claimed he could show them where he had left her body.

This was someone who had never been on police radar. At the time of Chrissy's disappearance, Ringel had been 24 years old.

Despite this confession, justice remained elusive. Due to police mistakes during Ringel's interrogation, a judge threw the case out in 2006. The case was stayed for a year, but with no new evidence emerging, Ringel walked free.

Enter David Ridgen. In 2009, after learning about the case, Ridgen began working with Mary Ann Harron. Through Freedom of Information requests, they uncovered court files and investigative documents that revealed why the first case had failed. His work initially focused on creating a television documentary for CBC.

"I recall Chrissy's case made the short list pretty much right away for several reasons. I attended a memorial service for her in Hanover... and something about the service for her, her photo up there on the stand, how people spoke about her. The whole atmosphere was very thick. It made me want to try to help," Ridgen shared on the podcast.

Watch: Robyn Howarth on the Faraday kidnapping. Post continues after video.

The emotional weight of the case hit him hard: "And I remember actually crying, and I remember feeling this kind of heat of frustration about the case, you know, I just, I just kind of knew that I wanted to help."

In a bold move, Ridgen even tracked down Anthony Ringel: "I do meet him. I knock, cold knock on his trailer door at a trailer park. We speak for a long time, and I ask him the direct and pointed question: Did you kill Christine?"

We hear the answer, he says, in the CBC documentary.

Shortly after it aired in spring 2012, police launched an undercover operation targeting Ringel. This operation captured footage of Ringel describing in disturbing detail how he suffocated Chrissy by pushing her face into the mud, used her jacket to restrain her hands, and concealed her body. He even spoke about contemplating doing it again, with a twisted justification that by "only doing it once," he had somehow been a "good person."

Ridgen believes his documentary exposing police errors was the catalyst for this undercover operation. He said: "I can only assume that it had something to do with it, because basically the documentary exposes a ton of police errors and mistakes, and it's very embarrassing for the OPP" (Office of Public Prosecutions).

The evidence gathered during this operation led to Ringel's second arrest in February 2013. This time, the trial in 2016 resulted in his conviction for second-degree murder, for which he received a life sentence. But justice, in this case, remains incomplete; Chrissy's body has never been found.

Mary Ann wasn't allowed to sit in court during the second trial as she was considered a potential witness. Later, Ridgen played some of the undercover videos for her, though he spared her from the most graphic content.

"It is heartbreaking, and it's awful, and Mary Ann wanted to see it, and I still didn't show her, she knows this, I didn't show her everything, because some of it is just too it's really hard," he explained.

Despite Ringel's conviction, Mary Ann has stated that even his life sentence doesn't bring closure.

As Ridgen puts it, "I think closure's bullsh*t myself, and I think Mary Ann kind of agrees, but I think it's kind of a media presentation... I think it's more acceptance that you're looking for... but she wants to know where Chrissy is... They just want to know where their loved one is. They want to know where their daughter is."

Today, nearly 10 years after Ringel's guilty plea, David Ridgen continues to assist Mary Ann in searching for Chrissy's remains. They've used cadaver dogs in the area where Ringel indicated he left her and plan to return when conditions are more favourable.

As for Ringel, Ridgen believes he will eventually be eligible for release. But that won't stop Ridgen's quest for the full truth.

"I think that eventually he will get out... Once he gets out, he'll be in the community again," he said. "He'll be right back, probably in the same trailer park, and I'm just going to go back up and knock on the door. If I'm 80, I'll do it… it's also part of the promise that I make."

Feature Image: Instagram/CBC/CBC Podcasts