If some policeman were to consider this, I suspect that they know it would not be good for their career. And they know that there are some (presumably ineffective) Internal Review Board processes. But if you did arrest another officer for committing a crime right in front of you when the whole world is watching, you would have another career. For example, you could be invited to lectures at many colleges for some years.
I think that any cop that does this would want to be smiling, quiet, and polite through the whole process. I recently asked a Military Policeman at some bar if he had ever prohibited a general from entrance onto his facility. (I know there are processes and paperwork to get a visit approved.) He told me, "No, but I did forbid a major the other month." And he told me that his amusement with the major's assertions was increased by smiling the whole while.