First, you need to demonstrate that there is a statistically significant difference in the rates of death penalties. Then, you need to provide evidence that any statistically significant difference is due to racism. Only then, can you even begin to discuss whether the observed racism is "institutional" or not.
So, where do your numbers come from? This one might be interesting to study.
Whether his example is actually due to racism or not, it's still irrelevant for determining if it's institutional or not. I don't think judges or juries are encouraged by the system to give the death penalty to Blacks 3:1. If the decisions are based on race, it is because of their own individual biases. Again, a plurality or even majority of opinions doesn't make it institutional. There has to be an institution first.