ON APRIL 20, 1999, Eric D. Harris, eighteen, and Dylan B. Klebold, seventeen, carried an arsenal of weapons into Columbine High School in Littleton, Colorado. With two sawed-off shotguns, a semiautomatic handgun, a semiautomatic carbine, and several homemade explosives, these two high school students ran rampant throughout the school, shooting at students and teachers alike.

Harris and Klebold killed thirteen people, including twelve of their classmates and one teacher. Then they killed themselves. Harris, Klebold, and all who died in the Columbine tragedy are among the nearly thirty thousand Americans who die from gun violence each year.

Where did they get their guns"

After the Columbine shooting, investigators discovered that the majority of the weapons the boys used originated from gun shows. Harris and Klebold bought the TEC-DC 19 semiautomatic handgun from twenty-two-year-old Mark Manes. Manes had legally obtained the gun at a gun show and then illegally sold it to...