Abba_S:
You’re so lucky you get to learn each day. I hardly know which way to operate a Gemarah!!
#1) Must be firsthand knowledge.
#2) Exactly as you wrote
#3) Also as you wrote – that is the ????? condition
#4) Read my apology above!!
#5) The condition to do it openly – because otherwise people would suspect you’re only gossiping. People are going to suspect you, and also the objective won’t be realized – for others to take note and do what’s necessary.
Note – these are all for sins of bein adam lamakom, as explained earlier.