Some of the deadliest mass shootings around world

Rachel Ruth, left, Rhianna Cheek, center, and Mandi Annibel, all 16-year-old sophomores at Heritage High School in Littleton, Colo., console each other during a vigil service in Denver's Civic Center Park late Wednesday, April 21, 1999, to honor the victims of the shooting spree in Columbine High School in the southwest Denver suburb of Littleton on Tuesday, April 20, 1999. (AP / Laura Rauch)

A gunman at a Connecticut elementary school killed more than two dozen people, including children, on Friday. It is among the world's worst mass shootings. Here is a look at some others: