Semantics... We likely agree on the other officers' responsibility/duty both to police the unlawful/unjustified actions of their colleagues and to protect the life and liberty of Mr. Floyd in this situation.

I think murder requires some threshold of intent deliberation and I'm not very familiar with the details in this incident just yet... but on it's face it's doubtful the officer intended to kill George Floyd and choose a slow, public asphyxiation concealed by the unreasonable/illegal restraint while having him legally detained as a forgery suspect. That, of course, doesn't absolve him of being directly responsibility for this man's death.
They are not being charged (yet) because: it's only been a few days, only a very small percentage of crime commission results in charges, having charges at this point in time would have required the suspects to issue charges against themselves/each other and if one of them had that much integrity, George would probably not be dead in the first place, convicting the officer of murder may be difficult, so accessory or accomplice charges will require careful deliberation, information still being gathered, among other reasons.

FWIW, the people filming and/or spectating as George Floyd was killed bare some moral/ethical responsibly for their lack of (or cowardly?) effort to physically interject, although I'm aware many will not agree with me here.

Concerning Tamir Rice, a person called in to report 'a man in a dark hoodie at the park playground, waiving a handgun around pointing it at kids, they think it might just be a realistic looking toy gun' or similar to 911. The dispatcher called a unit to respond but did not include 'think it may be a toy gun' portion of the callers request for a police response. The officer spotted Tamir, standing alone, from 100 yards or more across the open field in the park. The one driving speeded across the field toward Tamir and pulled up close with officer Tim Loehmann in the passenger side, putting him directly in front of Tamir. Allegedly Tamir brandished/pointed/pulled out the gun and officer Loehmann fired in response and fatality
wounded/killed the young boy. It was tragic and there were dangerous mistakes made by multiple people but charging the officer who gunned Tamir down with murder would have almost surely resulted in acquittal. Mr. Loehmann then fraudulently concealed his background and got hired as a rookie officer in a small town across the state, then was subsequently fired upon discovery of his past.

The amount of violence, fear, division and destruction I have witnessed in the name of 'Justice for Tamir Rice' is also tragic. Protesters blocking roadways, terrorizing restaurant patrons and vandalizing or destroying uninvolved businesses every time someone else with a similar color skin dies unjustly does not help prevent the CPD from shooting innocence black children.

It seems that 'rules of engagement' between police and civilians have been eroded over time while executive authority has been expanded. This current state of anarchy can be greatly improved with discussion, consensus, enforcement, and public awareness of these rules. Until then some police will continue to act like mobsters and most will accept, take advantage of or enable some level of legal privilege because of their position. Body cams show us that unequal, crony, illegal, racist, and biased enforcement is widespread. Police in America conduct silent home invasions for non violent drug charges, shoot innocent people and pets without consequence (sometimes at a mistaken address), routinely profile otherwise cooperative non violent people as a threat in order to unlawfully discriminate. They point guns at these threatening people with impunity and treat them as hostile while being so threatened by guns that they can justify driving up to a 12 year old in a park with a fake plastic gun and open firing, no words exchanged. This is an area where legal reform and awareness severely needed.

Burning down Wendy's may have influenced a reactionary, politically motivated, premature legal filing. It will probably compound the hardship of those peoples and family's whose jobs and paychecks were destroyed. It will surely hurt a struggling economy and further stress the community by destroying a busy, low-cost prepared food resource and it will deprive the Dave Thomas Foundation of all future donations during a time of intense need.