If the prosecution can identify multiple elements to each criminal "transaction", they would have multiple elements of their case to prove successfully but if they do it results in multiple charges, each for a different element of the same incident.
That is what has happened here. There was a LOT going on, from the knee hold on a man who had already stopped resisting, to the neglect of medical attention, to the police protocols he had violated - and if there are three distinct ciminal aspects to the same murder, then he gets three distinct criminal convictions for the same murder.
This is not unusual. It's normal legal practice in America and internationally.
Caption this Meme 