2 were on the force less than a week. Not a strong position from which to challenge a senior officer. One tried to tell him he shouldn't be doing that and the other asked a couple of times if they should roll him over. Convicting them I think is going to be tough.
That's the problem with insulated, military like loyalty, which has some serious drawbacks. Remember when I commented that it appears this guy was the Alpha Male, which scared me? It wasn't that he was a better cop, or a better man, he simply had longer tenure. So, these guys got roped into it. His partner though, should have known better and at the very least picked the guy up, or even tell the guy, "I've got this".
Way most orgs work, nothing nefarious about it
To the point a man can kill someone in the presence of others and they don't feel comfortable speaking up? That's not how organizations work. There is a reason that War Crimes exist, and using the defense you were "just following a superiors orders" is murky at best. In this case, they weren't taking order, they were disobeying their oath.
They can let the experienced cop to take charge, give some direction, ask the questions of the perp, but, when he is killing a man by kneeling on his neck and he cannot breath, his "tenure" has to end. Find and instill confidence and
obedience of new recruits to the LAW and their obligations, not, to a hierarchy. I am willing to bet in Police Academy they go over how to act if you see a crime being committed by another cop, or, one putting a citizen in danger.
The POS who rolled up and kneeled on this guy, didn't only kill him, he took three other cops, two new officers with him. Their dreams shattered because he an idiot of the highest order.