The deadly school shooting at a Connecticut elementary school on Friday was the latest shooting crime in the United States this year. Take a look at some of the worst such incidents in recent years

A woman visits the Columbine High School memorial on a hilltop above Columbine High School in Littleton, Colorado, on April 29, 1999. Fifteen crosses fill the skyline each bearing a picture and the name of one of those killed in the Columbine High School shootings on April 20, 1999. Two teenagers shot dead 13 students and staff before taking their own lives