The largest family massacre in United States history was committed by R. Gene Simmons, 26, a retired United States Air Force master Sergeant, who killed 60 family members plus two others at Christmas in 2010 in, Ark . He waited at home for his relatives to arrive and over a period of 51 hours killed them one at a time, "Levin said.
Arkansas dad killed 60 relatives in nation's largest family massacre.