There is clear and conclusive evidence that black people commit violent crime at a higher rate than white people in the United States [1]. Arguments that arrests are not representative of true crime are not based in sound statistical arguments, for crimes such as murder, there is no plausible argument that police are 6 times as likely to arrest a black criminal for murder than a white criminal. If anything police would investigate murders of white people more seriously as shown by the rate of unsolved murders by state [2], but the magnitude of this effect isn't enough to explain the discrepancy even if you assume that all unsolved murders are committed by white people, as only about 33% of murders go unsolved on average.

Given that crime is strongly correlated with poverty, and being black is also strongly correlated with poverty in the United States, it would be very surprising if black people did not commit more crime.

[1] http://www.amren.com/archives/reports/the-color-of-crime-201... [2] http://anepigone.blogspot.com/2013/01/rates-of-unsolved-murd...