The problem is, this death was a result of systemic problems between the police and society at large, specifically the police thinking - correctly, it appears - that they're above the law.
The lack of prosecution in this case is NOT because the police are "above the law". The lack of prosecution in this case is because the law specifically allows the police to use electronic devices in the course of their duties while operating their vehicles. The same way the law allows the police to exceed the speed limit in certain cases, or allows them to park pretty much anywhere, or allows them to pull you over, or allows them to do any number of other things that a normal citizen can't do.
You may argue that it's a bad practice, but keep in mind that one person dying because officers are allowed to use electronic devices while driving doesn't necessarily mean that's bad practice any more than officers sometimes causing accidents because they can speed or run red lights in the course of their duties means those are overall bad practices either. We'd need to know how many people are hurt as a result of officers operating electronic devices while driving and compare that to how many people would be hurt if officers had to use the radio or pull over every time they needed to use electronic devices.
Regardless, there was no legal basis for criminal charges in this incident.