Profile of homicide victims
Data here. The vast majority of homicide victims have criminal records, usually extensive ones, and the trend has been increasing:
"In Baltimore, about 91 percent of murder victims this year had criminal records, up from 74 percent a decade ago, police reported. In many cases, says Frederick Bealefeld III, Baltimore's interim police commissioner, victims' rap sheets provide critical links to potential suspects in botched drug deals or violent territorial disputes... Philadelphia also has seen the number of victims with criminal pasts inch up, to 75 percent this year from 71 percent in 2005, department statistics show.
In Milwaukee, ... 77 percent of murder victims in the past two years had an average of nearly 12 arrests."
Hat tip to Joe Olson, who pointed out that Don Kates has been studying and documenting this fact for about thirty years, with little coverage in the press.