Dylann Storm Roof is accused of opening fire at a church in Charleston, South Carolina, killing nine.
Dylann Storm Roof is accused of opening fire at a church in Charleston, South Carolina, killing nine.
Chuck Burton/AP
Adam Lanza killed 20 children and six adults at Sandy Hook Elementary School in Newtown, Connecticut, in 2012. He also killed his mother.
Adam Lanza killed 20 children and six adults at Sandy Hook Elementary School in Newtown, Connecticut, in 2012. He also killed his mother.
Rex USA
James Holmes opened fire inside a packed movie theater in Aurora, Colorado, also in 2012. He killed 12 people and injured 70.
James Holmes opened fire inside a packed movie theater in Aurora, Colorado, also in 2012. He killed 12 people and injured 70.
Andy Cross/The Denver Post/Getty Images/File
Jared Loughner killed six people and wounded former U.S. Rep. Gabrielle Giffords in Arizona.
Jared Loughner killed six people and wounded former U.S. Rep. Gabrielle Giffords in Arizona.
Pima County Sheriffs Office
Seung-Hui Cho was responsible for the 2007 massacre at Virginia Tech, which left 32 people dead.
Seung-Hui Cho was responsible for the 2007 massacre at Virginia Tech, which left 32 people dead.
Virginia Tech/Getty Images
Aaron Alexis killed 12 people inside the Navy Yard in Washington in 2013.
Aaron Alexis killed 12 people inside the Navy Yard in Washington in 2013.
FBI
Eric Harris and Dylan Klebold were responsible for killing 13 people at Columbine High School in Littleton, Colorado, in 1999.
Eric Harris and Dylan Klebold were responsible for killing 13 people at Columbine High School in Littleton, Colorado, in 1999.
Columbine High School/AP