Deputies found the two along with their son, Jonathan, dead inside.
For three days Don Ritter's son, daughter-in-law and grandson were dead right next door without him even knowing.
"This is what I say: there were three dead people laying over there that I had no knowledge -- wasn't aware of," says Ritter. "I cannot make no sense of what went on."
He says the Garland County sheriff's Office told him his 23-year-old grandson shot and killed his parents then turned the gun on himself.
"Not real easy," responded Ritter when asked how he's handling the situation. "When something like this comes out of the clear blue sky for no reason at all."
Neighbor and former coworker of David and Jonathan, Christopher Chamberlain says the sound of gunshots in the area are fairly typical out in the county.
"Saturday evening, working in the yard and I heard gunshots coming from this direction," he pointed toward the Ritter house. "I kinda wish I had called somebody about it."
Chamberlain didn't think anything of the gunshots until deputies showed up for the welfare check and he heard it on the news.
Having worked with both Jonathan and David in the past Chamberlain says he thought David was a bit hard on his son.
"Him and his dad fought kind of regularly," mentioned Chamberlain. "I hate to hear that his mom was drug into it and was killed as a result of it. Man that's just awful."
Ritter says his son, David, was well liked by friends, family and coworkers.
"He was, well, let's put it this way: Everybody loved him," explained Ritter.
As for his grandson Jonathan, "He wouldn't say a lot. He was kinda quiet," shared Ritter. "But that was the last thing that you could've figured to come out of him."
Now Ritter is left to wonder exactly what happened and why while acknowledging he may never know.
"Why would he want to take his mother and dad's life and then his own?" asked Ritter. "It don't make sense."
According to the Garland County Sheriff's Office, at this point, there is no motive.
Copyright 2016 Nexstar Broadcasting, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.