We've seen plenty of movies, books and documentaries on serial killers, but not so many on those who are so efficient and deadly, that they can murder dozens of people in a single day. Murder sprees seem to have become more prominent over time; notably the tragedy in Norway which is as recent as July 2011. This evil act will no doubt happen again thousands of times in the future. What I have presented in this list is no more than the proverbial tip of the iceberg.