Have I ever arrested another officer? No. Have I reported bad seeds to the Sheriff's Office (the top law enforcement agency) in my county, since the my now former Chief was covering it up? Yes. Repeatedly. Have other good officers at my department reported the conduct to the District Attorney's Office? Yes.
Did it matter or amount to anything? NO. But it wasn't for lack of trying. As I said in my initial comment, I've seen good officers get shafted and bad ones skate, but I am not one to turn a blind eye to such conduct. The politics are thick on these things, in my opinion, the worst thing is fear of "bad publicity" if such things got known. Thanks for your questions, by the way. This is a particularly bad (for me) but important topic.
Aren’t you charged with arresting criminal you observe committing crimes? Aren’t you failing in your duty when you don’t protect the public by letting dangerous criminal commit criminal acts in front of you without arresting them?
Nice story about telling this or that official. You are the official empowered with arrest powers. If you had arrested such criminals when you observed such criminal behavior, then the DA would be forced to publicly decide whether to charge them or not. In addition the criminal would have an arrest record. So do your job.