The jury did not let him off because 'killing a black guy is no big deal.' They found him innocent of charges based on the evidence that was presented to them. Systemically, I agree there are problems, but unless people come up with a solution that works, there's really no way forward. Most people have really basic (meaning poor) understanding of the data surrounding cop shootings and immediately blame it on race when there are other complex factors involved. If you are curious about some of the nuance around this topic, here is a good article by a balanced source: http://www.nationalreview.com/article/437651/police-killings-racial-bias-not-proven

I would say that the two biggest valid systemic racism issues happening today in our society/legal system that has to do with race are drug laws and racial profiling. My solution to the former is to 'legalize it,' my solution to the latter is 'there is no solution until other social/cultural disparities start to even out.'