They left the couple and their son and daughter to die, but the children miraculously survived.
Brooks Douglass is one of the survivors. He was 16 at the time and he went on to become an Oklahoma state senator.
Douglass' story became the subject of a movie "Heavens Rain."
The killers, Steven Keith Hatch and Glenn Burton Ake, were arrested at a Colorado ranch five weeks after the shooting at the Douglass home.
Both were sentenced to death.
Hatch died by lethal injection in 1996.
But after numerous appeals, Ake's death penalty sentence for first degree murder was overturned.
He was instead sentenced to life in prison.
While serving as Oklahoma senator, Brooks Douglass came face-to-face with Glenn Ake.
Brooks was touring the Oklahoma state prison when he decided he wanted to meet Ake.
After the hour and a half conversation and Ake's apology for what he did to the Douglass family, Brooks says he told Ake he forgave him.
"Whether I liked it or I wanted to, I knew it was what I needed to do," Brooks says. "Once I did it, that was the moment that changed everything."
Now Brooks travels the country delivering his message of the importance and power of forgiveness.
"We're capable of doing much more than we necessarily think we are in terms of being able to overcome difficult things that happen in their lives, and we have a choice of how to deal with those things," he says.
Brooks delivered his message to soldiers at Fort Sill during a prayer luncheon.
He says his message is a good one for soldiers to hear, especially those who have been deployed and have seen or done things they wish they could forget.
"Ultimately if we can confront them and find a way to forgive them, then we can let go and really finally begin to live more complete lives," he says.
Brooks says he thinks about what happened to his family every single day.
But he says the murders of his parents shaped his life and made him determined to try to make a difference in the lives of others.
Ake died of a heart attack at a prison hospital last year.
Brooks says his little sister Leslie has had a hard time dealing with the murders of her parents, but he says now she's doing well.
She's living in the Oklahoma City area where she's a vice principal of a school.
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