IheartmyOscars

so, aren't you all so glad i've stumbled into this forum to ask you all my silly questions?
i have a puzzle of sorts for you. my previously mentioned 10 gallon with the tetras also houses a pleco (6 in or so) that will soon be moved to the 55 gallon. he was an orphan pleco, arriving in the murky waters of an abandoned 10 gallon someone dropped off for me. so in with the tetras he went, were he has been happily co-existing. we call him Bob. anyway, I also had 3 mollies in this tank, I realize this was quite crowded. the mollies turned out to be ill, (hole in the head for at least one of them) and while 1 floated dead to the surface, the other 2 simply dissappeared. not in the gravel, or the castle in the middle (I took it out and checked thoroughly). another year later and no other mysterious disappearances, until recently when i did a 50% water change in order to move the tank to another room. once i added more water and set everything back up, i lost a tetra. my roommate blames Bob for the missing fish, after all, he is the monster in the castle. i think it's impossible for my toothless herbavore to consume the other fish. am i wrong? was it Bob? or is my castle haunted? help!