Aiding and abetting requires two mental states. First, a person must know that someone is going to commit a crime. Second, the person must intend any actions to further that crime. So in this case, not only do they need to prove that these three other officers knew Chauvin was murdering Floyd, but also that their actions were with the intent to help Chauvin murder Floyd. Take note that these guys are charged with aiding and abetting an unintentional second degree murder though. Having mulled over the article I linked and after browsing some Minnesota statutes, I think the required intent for aiding and abetting second degree murder is going to be very difficult to prove against these guys.