Decided to look this up after the Arizona incident a few weeks ago. Mass murders are usually described as four or more murders in a particular location during a relative short period of time. There were three mass murders in 2010. Eight people were killed in Appomattox, Virginia on January 20, 2010. Nine people, including the killer were killed on August 20, 2010 in Manchester, Connecticut. Four people were killed in Buffalo, New York on August 16, 2010. (Fort Hood murders took place in 2009)
The person credited with killing the most was Mao Zedong (Chairman Mao). From 32 to 45 million people were worked, starved, or beaten to death in China during four years from 1958 - 1962. For comparison, the worldwide death toll of the Second World War was 55 million, and Hitler's total was between 11 and 17 million, While Stalin's number ranged between 20 and 60 million, but has not been completely documented.