The policemen did not stand by and watch the suspect beaten to death, simply because the man died days later... when the police were not there watching him die.
The police took him in about 2 minutes. Standing there doing nothing would be much longer than that.
The fact that the other four policemen are not charged is because America is a nation of law. There are people let go all the time who were at the scene of a crime, even from in the car or home of the offense taking place by another.
Did any of the other cops report the crime? If not they are guilty of Misprison of Felony, 18 US Code 4.
Oh come one...you and I have both seen what the victim looked like. Anyone who stood by while that happened and didn’t realize that 1) this is seriously wrong and 2)I better stop this now, is too stupid to be a cop. The victim was suffering life threatening if not life ending injuries.
Cops have a higher standard (or should) than the average citizen. They are supposed to serve and protect. They failed, but they not only failed, they passively empowered and therefore are guilty. Just like the driver of a getaway car.