"Certainly if he could reach that level of rage over a bag of potato chips, there's no telling what he's capable of"

Eventually, April Balascio would discover that her father, Edward Wayne Edwards, was a serial killer — and then she’d help bring him to justice.

But even before that terrible revelation, she and her siblings had discussed the fact that their dad had a dark side — which he sometimes took out on the family.

The case’s twists and turns (and Balascio’s central role) will be the focus of Monday night’s People Magazine Investigates, on Investigation Discovery, exclusively previewed above.

• For more on Edward Edwards’ dark secrets and his daughter’s search for the truth, subscribe now to PEOPLE or pick up this week’s issue, on newsstands now.

According to the clip, Balascio and her four siblings were discussing the killing of their adopted brother, “Danny Boy” Edwards, at one family gathering when talk turned to their mom’s hospitalization in 1982.

As Balascio learned, it was her father who put her there.

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Edward Edwards (left) in 2010
| Credit: Phil Masturzo/Akron Beacon Journal/AP

“Supposedly, the boys [my brothers] had eaten the bag of chips,” Balascio recalls in the preview.

Edwards “came home, he wanted the bag of chips, he was upset, ranting and raving,” she says. “Mom was trying to calm him down. He [grabbed] the knife, he stabbed her.”

• Watch the premiere of People Magazine Investigates: My Father, The Serial Killer on Monday, Jan. 15, at 8 p.m. ET on Investigation Discovery.

Of hearing about this violence, Balascio says, “I just couldn’t believe it.”

“I was saddened,” she says. “I was also shocked. I mean until that moment, I didn’t even know.”

PEOPLE Deputy Editor Dan Wakeford puts it another way in the clip: “Certainly if he [Edwards] could reach that level of rage over a bag of potato chips, there’s no telling what he’s capable of.”