They're on a mission in the name of their son to make sure this kind of violence doesn't happen again and to hold the parents of gunmen Eric Harris and Dylan Klebold responsible. They say this was a hate crime and there's still lots of hate in Littleton.
Last spring, they filed a $250 million lawsuit accusing the gunmen's parents of negligence. CBS News has learned the they've also added to the suit the names of the men who sold the gunmen their weapons.
CBS News Correspondent Russ Mitchell spoke with the Shoels and their attorney Geoffrey Fieger on CBS This Morning.
Why are they focusing their lawsuit on the parents?
"All parents are supposed to know what their children are doing at all times," says Michael Shoels. "I know itÂ's almost impossible sometimes to know everything they're doing, but knowing the creation of bombs, having weapons in their possession, I say they have to have some kind of responsibility."
Adds Fieger: "Can you imagine the parents of high school students who relinquish their home over to their students to amass an armory that would make a small army look proud? We understand one of the parents wasn't allowed in the garage because they were making propane bombs."
The Shoels pulled their two children out of Columbine, and with the help of a fund established for victims' families, left Littleton and relocated to Denver.
"I donÂ't know if it's a dangerous place," Vonda Shoels says of Columbine. "But my children are not interested in going back Â… they're scared of Columbine."
And Fieger says "The money isn't the issue. It never has been Â… We're looking to get to the root of this phenomena that has never occurred in America before: Children coming to school with guns and slaughtering other children."
In addition, Fieger points out, "Isaiah's murder at Littleton was racially motivated. They went looking for Isaiah. Isaiah was one of only a handful of African American students" at the school.
Since they filed their lawsuit, the Shoels have been criticized by some in Littleton who feel the community should be trying to come together right now.
"We were part of that community and felt very happy," says Michael Shoels, who adds that his house was vandalized three times before the shootings. "Under these circumstances, you know, it's kind of hard to feel like you're part of a community.
"I mean, we are all Americans. We're supposed to be able to stay where we want to."