In an exclusive interview with RadarOnline.com, Brad Bernall reveals he was "somewhat upset with the killers' parents that they didn't take an active part in their boys' lives" as he did with his daughter.
He gave an example of his feelings and how the murderers' parents could've done things differently.
"After she got in trouble, from that point on she had no privacy. She just didn't. We invaded her privacy. If the Columbine killers and other killers that did something like this, had their privacy invaded by their parents or whoever was watching them, a lot of the shootings probably could've been circumvented," he explained.
The heartbroken father detailed how the death turned his life upside down.
"It was the most painful thing that I ever had to endure in my life," he said. "And it was more then just mental, it was physical as well. My heart actually felt like it was swelling, and it pained inside my chest and I honestly thought it was going to kill me."
He came to his wits' end when he finally dropped to his knees turning to a higher power.
"'Lord I can't take this anymore. You got to take it away from me,'" Brad pleaded with his God. "And truly — this is no exaggeration or embellishment — the terrible terrible pain, the physical pain that I had, it just went away. It was just gone."
That's when he says the unrelenting agony subsided and he "was pretty much at peace then."
"At that point the heavy grieving, the crying and the sobbing that a person does that totally expels the air out your lungs, that will suffocate you was over. It was a truly a miracle."
"I think of Cassie every single day," Brad told Radar exclusively of his daughter who was tragically killed on that horrific day.
But he says there's still pain that lives inside of him. "I don't anticipate that pain ever leaving and I imagine other parents who feel the same way."
He reiterated his beliefs that the parents could have possibly prevented the demise of his daughter and so many other children on April 20, 1999. "I think a lot parents back off on the parenting job and allow too much freedom and privacy too early. That's my message. If everyone realized that and acted upon it a lot of these things wouldn't happen."
"This year for the 20 year anniversary we are taking a family vacation," he said.
Saturday, April 20 marks the 20th anniversary of the Columbine shooting. It was one of the deadliest mass shootings in U.S. history..
On that day, armed students Dylan Klebold and Eric Harris went on a mass killing spree on their Littleton, Colorado campus, killing 13 people and injuring another 23 before turning their guns on themselves.