On Friday, June 20, 1913, 100 years ago, death arrived at the Marienschule school in Bremen, Germany. What happened that day wasn't just any old murder -- it was the first documented mass school shooting in history.

It was shortly before 11 a.m., as teacher Maria Pohl lined her students up in two lines to leave the school building for recess. As the girls began to move, a man stormed up the stairs and opened fire. His name was Heinz Jacob Friedrich Ernst Schmidt, a 29-year-old unemployed teacher who had only lived in the city since December of the previous year.

Panic broke out as Schmidt continued to fire his gun. Two girls were shot dead. A third fell and broke her neck as she tried to climb over a stair railing to escape. A few other girls retreated back into the classroom, where they were pursued by the killer. The five- and six-year old girls begged for their lives: "Uncle, please don't shoot us!"...