16 years ago today, the country was rocked by one of the worst school shootings at the time when two high school students brought weapons into Columbine High School in Littleton, Colorado and opened fire. Today, the victims of the shooting are being remembered as the school is closed, as it has been every year since.

On the anniversary of the attack that left 13 people dead and more than 20 others wounded, the high school is observing the day as it has every year by being closed for the day, ABC 7 News reports.

The principal at Columbine, K.C. Somers, sent home letters to students in early April to let them know they would continue the tradition of being closed “out of respec”t for the lives lost that day.

A moment of silence was planned to remember the victims, led by Frank DeAngelis, the former principal who was there that day and retired last year.

Fox 31 Denver reported there will be an event called Run for Remembrance to be held on May 2.

The victims in the attack were Steven Curnow, Daniel Mauser, Isaiah Shoels, Lauren Townsend, Kyle Velasquez, Cassie Bernall, Matthew Kechter, Corey DePooter, Kelly Fleming, Daniel Mauser, William “Dave” Sanders, Daniel Rohrbough, and Rachel Scott.