Bureau of Justice Statistics,,
Homicide trends in the United States,,
www.ojp.usdoj.gov/bjs/homicide,,
Date of release: January 17 2007,,

Percent of Homicides with Multiple Offenders and Victims,,

Year,Offenders,Victims
1976,11.5,3.1
1977,11.2,3.3
1978,11.6,3.1
1979,12.3,3
1980,11.8,3
1981,11.9,2.9
1982,12.3,3.2
1983,12.1,3.2
1984,12,3.2
1985,12.1,3.6
1986,12.4,3.5
1987,12.6,3.5
1988,15.5,3.3
1989,15,3.6
1990,17.4,3.6
1991,18.7,3.1
1992,17.6,3.9
1993,18,3.8
1994,18.3,4.2
1995,18.2,4
1996,18.9,4
1997,18,4.3
1998,18.4,4.1
1999,17.6,4.8
2000,19.3,4.3
2001,19.1,4.5
2002,18.8,4.9
2003,17.7,4.9
2004,18.7,4.5
2005,20.3,4.4

"Source: FBI, Supplementary Homicide Reports, 1976-2005",,
See the methodology section in 'Additional Information About the Data' for weighting and imputation procedures used.,,