if you have lr you have bristle worms. if you are going to have a trigger i would stick to large angels, tangs, eels, puffers, rabit fish, and puffers. maybe not so much the rabit fish it depends on what your trigger is like.
try leaving a fish trap out over night and see if you get some thing in the morning. if it was the trig you would see half a dead fish somewher in your tank.
i doubt the humu trigger did it. ive seen my humu trigger kill befor. its pritty horrible, when my trigger wants to kill a fish he goes right for the gut sack rips it open and then lets is die. then if he wants to eat it he only eats like half befor he is full. and ther will be a lot of left...