Keep in mind that the heart has to be pumping in order to pump blood and lymph into crushed tissue in order to make a bruise.
If he was shot 2 seconds after the baton strike, I can't imagine there would be bruising.
I don't know the state of the science, though. I wonder if medical examiners can detect damaged tissue microscopically.
Also, do we know if the baton strike was solid, light, or glancing?
I'm not saying there weren't problems with this shooting. I'm saying this might not really be evidence of a problem.