Pam McClain is no quitter.
When her daughter Joyce went missing on August 8, 1980, and was found dead two days later behind her local high school in East Millinocket, Maine, Pam wanted answers.
Police interviewed dozens of potential suspects, including out-of-towners and locals, but came up empty — for years.
But Pam, now 71, never gave up, pressuring police to keep working the case and keeping the murder in the public eye.
“It was 38 years of my lifetime that I fought for Joyce,” she tells PEOPLE.
The decades-long mystery is examined in-depth on Monday’s episode of People Magazine Investigates on Investigation Discovery. The episode, “Murder Among Friends,” airs on Dec. 10 at 10 p.m. ET. (An exclusive clip is shown above.)
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The show chronicles Pam’s relentless pursuit of justice.
“I wasn’t going to give up after 25 years, 30 years, 35 years,” she says. “I thought, ‘I’ve come this far. I can’t stop now.’”
When the case was finally solved, Pam was able to grieve her daughter for the first time, she says. “In all those 38 years with trying to get Joyce’s [case from] unsolved to solved, I didn’t have any time to grieve,” she says.
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The journey to justice, she says, has “been hard on me.”
But the solving of the case took “a weight off my shoulders and off my brain,” she says.
“We pushed, we solved it…. We are so full of peace.”
People Magazine Investigates: Murder Among Friends airs Monday, Dec. 10 at 10 p.m. ET on Investigation Discovery.