The ME said something criminal happened, moy thinks there wasn't, therefore he thinks the ME was wrong. This is where the argument is now, a medical examiner was incorrect.
Also, Mike posted an article that states that it's incredibly common that prosecutors go easy on cops because they work with them, and they see it as a conflict of interest. So yes, there's an obvious possibility that while there was evidence that suggested there absolutely should be a trial, the DA didn't choose to pursue it for that reason.