American Roulette: Murder-Suicide in the United States / Violence Policy Center, April 2008
http://www.vpc.org/studies/amroul2008.pdf
"At least 554 Americans died in murder-suicides during the first six months of 2007 with the vast majority (88.5 percent) involving a firearm, according to the third edition of the Violence Policy Center’s (VPC) study American Roulette: Murder-Suicide in the United States."