I have read comments and articles (an example) that claim that African-Americans are responsible for more than 50% of all homicides in the United States of America.
How credible is this claim?
Yes, according to the US Department of Justice document Homicide Trends in the United States, 1980-2008:
Table 7, Homicide type, by race, 1980-2008:
Homicide offenders were:
Felony Murder Offenders were:
The report makes the following statement about potential bias due to unknown information:
While many agencies report supplemental data on homicides, much of the data concerning offenders may not be reported because no suspects were identified or the agency chose not to report the information. The most significant problem in using SHR data to analyze offender characteristics is the sizable and growing number of homicides in the data file for which no offender information is reported. Ignoring these homicides with no offender information would understate calculated rates of offending by particular subgroups of the population, distort trends over time among these same subgroups, and bias observed patterns of offending to the extent that the rate of missing offender data is associated with offender characteristics.
To adjust for homicides with no offender information, a method for offender imputation was devised that uses available information about murder victims for which corresponding offender information was provided as well as those with missing offender information. Through this imputation algorithm, the demographic characteristics of unidentified offenders were inferred on the basis of similar homicide cases—similar in terms of the victim’s demographic profile, circumstances of the homicide such as felony or argument, location of the homicide (region and urban), gun involvement, and year of the offense— for which offender data were provided. In other words, unknown offender profiles were estimated based on the offender profiles in offender-known cases, matched on victim age, sex, and race; circumstances of the homicide; location of the homicide; gun involvement; and year. Offender-based estimates in this report were imputed using this procedure. Other estimates in this report were based on homicides with known attributes, unless otherwise indicated. An estimated 30.8% of homicides involved an unknown number of offenders. For these homicides, the offender imputation method conservatively assumed the number of offenders to be one, likely resulting in an undercount of the number of homicides involving multiple offenders.
All rates were calculated using the estimated number of homicide victims or offenders as the numerator and dividing by the U.S. resident population estimates for the appropriate groups or subgroups. This report used bridged-race population estimates developed by the National Center for Health Statistics and the U.S. Census Bureau.
The report also finds that people are overwhelmingly being killed by members of their own race:
84% of white victims were killed by whites
93% of black victims were killed by blacks
For 2013, according to the FBI's Expanded Homicide Data Table 3-"Murder Offenders by Age, Sex, Race, and Ethnicity 2013 ":
out of 14,132 offenders:
5,375 Black or African American
This gives approximately 54% of "Black or African American" known offenders.
A different table from the same source, gives a subset, specifically one-victim one-offender murders, of the above set:
2698 Black or African American
(here "Unknown" means age and/or sex but not race is known, there are really many more unknown offenders)
For this subset, the figure is 48%.
Unlike the Justice Department figures, there is no attempt to correct the FBI data for the bias of the unknown fraction of offenders, which is about 1/3 of offenders.