"...underage...porn" these two words should resolve your thread title.
so maybe your dilemma isn't a moral one. According to your comments here it seems more to do with protecting your identity, job, or what?
child porn is in the category of black and white right and wrong. Accessing it on a computer makes one an accessory to a heinous crime. Get your evidence together and turn his sick ass in! I would not wait one minute. If you don't get any response from local law enforcement go to the media. Screw the WatchTower Bible and Tract Society. As you have found out, they do not CARE!