From Columbine to Aurora, the Denver area is often plagued by gun violence

Emergency workers tend to the wounded at a triage site near Columbine High School in Littleton, Colo., on April 20, 1999.

A week after the Columbine shooting, a woman looks at crosses posted on a hill above the high school.

An aerial view shows the crowd at the April 25, 1999, memorial in Littleton, Colo., for those slain at Columbine High School.

Police stand outside a Century 16 movie theatre in Aurora, Colo., after the shooting there on July 20, 2012.

Police investigate the suspect’s car outside the movie theater after the 2012 shooting in Aurora, Colo.

People come together during a public service across the street from the movie theater in Aurora, Colo., where 12 people were killed July 20, 2012.

Arapahoe High School students cross the street in front of their school on Jan. 7, 2014, the first day of classes after a fatal shooting at the campus.

A police officer hugs his kids after they were evacuated to the Recreation Center at Northridge after a shooting at STEM School Highlands Ranch on May 7, 2019, in Highlands Ranch, Colo.

Officials guide students toward a recreation center where they were reunited with their parents after a shooting at a suburban Denver middle school not far from Columbine High School. Several people were wounded and two students were taken into custody, authorities said Tuesday, May 7, 2019. An 18-year-old male student was killed, a sheriff said.

A teacher raises her arms as she exits the scene of a shooting at the STEM School Highlands Ranch on May 7, 2019, in Highlands Ranch, Colo.

Parents comfort each other at the scene of a shooting at the STEM School Highlands Ranch on May 7, 2019, in Highlands Ranch, Colo.

Students and teachers raise their arms as they leave the scene of the shooting at the STEM School Highlands Ranch on May 7, 2019, in Highlands Ranch, Colo.

Officers patrol the scene of a shooting at the STEM School Highlands Ranch on May 7, 2019, in Highlands Ranch, Colo.

Armed police officers and others are seen outside STEM School Highlands Ranch, a charter middle school in the Denver suburb of Highlands Ranch, Colo., after a shooting Tuesday, May 7, 2019.

Students are reunited with their parents after being evacuated to the Recreation Center at Northridge after a shooting at STEM School Highlands Ranch on May 7, 2019, in Highlands Ranch, Colo.

Students and teachers leave the scene of the shooting at the STEM School Highlands Ranch on May 7, 2019, in Highlands Ranch, Colo.