Ten points for best answer; One neon tetra dead: Who is the murderer?

Bloating can be a symptom of a lot of things. I'm uming you just found the neon dead? It may not be anyone killing it...just a dead fish, for any of an almost innumerable possibilities. I would, however, look into rehoming those clown loaches before they get too large, and you end up with more "mysteriously" dead fish, as your water quality degrades. I'd leave your current stocking level at what it is now that the gourami is gone (and after you rehome those clown loaches), or perhaps add a few more neons.