Her Husband Began an Affair with His Best Friend's Widow — That’s When She Began to Suspect Something Far Worse (Exclusive Clip) By Sean Neumann 18

Kathy Aldredge felt vindicated in front of the camera, finally free to share the truth about a devious plot she quietly investigated — at times alongside police — for the better part of the last two decades.

“I feel a lot of satisfaction,” Aldredge tells PEOPLE. “I’ve waited a long time to speak on this topic and speak about my experience, and so there’s a lot of satisfaction in finishing the project.”

Aldredge’s tireless search for the truth about her close friend Mike Williams’ mysterious 2000 death is at the center of ABC News Studios’ upcoming true crime docuseries, Mr. & Mrs. Murder, which begins streaming on Hulu on July 30. (An exclusive clip is shown below.)

The four-part series examines Williams’ disappearance the weekend before he and his wife, Denise, were set to celebrate their wedding anniversary — and follows Aldredge’s determined quest to uncover what really happened.

The 31-year-old father went missing after setting out on his boat to go duck hunting on the morning of Dec. 16, 2000, on Florida’s Lake Seminole. He never returned, leading police to later theorize he had been eaten by an alligator. But Aldredge grew suspicious after her husband, Brian Winchester, began having an affair with Denise — his best friend’s widow. She and Winchester eventually divorced but remained in each other’s lives because they shared a child.

“To say they stabbed me in the back doesn’t even touch it,” Aldredge says in the docuseries’ trailer. “They had stabbed me in the soul.”

She and Williams’ mother, Cheryl Williams — who adamantly believed Denise and Brian had killed her son — began digging deeper into what had happened. They ultimately worked directly with police, went undercover, and later testified against Brian and Denise when the pair were convicted of working together to kill Mike.

“I’ve been able to kind of shut the door on that chapter, but there’s a window that’s still open,” Aldredge explains to PEOPLE, wondering how Brian and Denise were able to get away with the murder for 17 years before eventually being convicted.

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With the docuseries is coming out soon, Aldredge says she hopes it might lead to others coming forward with more information about what happened — and why she believes police investigations into Mike’s murder were repeatedly halted. “I feel like there’s still some missing pieces,” she says. “I feel like Brian and Denise, for all those years, were protected in some way.”

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Aldredge says revisiting her experiences “took me back to a dark place.” After she and Williams’ mother, Cheryl, came forward with their accusations against Brian and Denise, they encountered police roadblocks — and backlash from community members who defended the couple.

Despite the blowback, the pair of fiercely determined amateur investigators never stopped trying to figure out how and why Mike was killed.

“She and I spent a lot of years under the radar,” Aldredge says, recalling the many days she and Mike’s mother spent digging for clues that might help connect the dots in his death. “Cheryl and I went through this together, even though we didn’t see each other every day and we didn’t talk every day, whenever we got together, this investigation was what we talked about. This investigation was what connected us, and it was a constant obsession throughout all those years, no matter how much time had passed between us, there was always that connection.”

Viewers can watch how it all unfolded on July 30 when Mr. & Mrs. Murder — which is produced by Plum Pictures and ABC News Studios — begins streaming on Hulu.