Bernardo Tobar, 22, son of an Olympic sharpshooter of the same name, was found to have acted in self-defense in the apparent kidnapping or robbery attempt and faces no charges, prosecutors said.
He was returning from the target range Thursday night along with his father, mother and 12-year-old sister when three men in a taxi blocked the road, he told police.
When two of the men pointed their revolvers at the group, the younger Tobar grabbed his .22-caliber target pistol and shot them.
The slain men, both of whom had criminal records, had fired their weapons, police said.
It was not immediately clear what happened to the third assailant. Tobar, a top Colombian national shooter, is following in the footsteps of his 49-year-old father - a top 10 finisher in Olympic rapid-fire pistol shooting since 1984 who is training for the Sydney Olympics.
The killings Thursday night happened in Jamundi, a municipality where leftist rebels and right-wing paramilitary fighters roam.
So far this year, two Colombian world-class cyclists, Oliverio Rincon and Luis Herrera, were kidnapped and later released. Rincon was held for a month.
Last weekend, leftist rebels kidnapped a former national soccer team member, Andres Estrada. He was released two days after a national cry of outrage.
National sports committee officials told The Associated Press that worsening violence was threatening an international rollerblading competition and could force the Copa America soccer championships next year to be moved from Colombia.
"Slowly, they're going to take us out of everything," Andres Botero said. "We're going to the pariahs of the Americas."