You know, I can't help but feel that Poe, little weirdo that he was, wrote this story fantasising that the victim was someone of his acquaintance. It's a creepy little story, but I think what makes it work is that there's no real reason given for the actions of the protagonist. He murders a man he knows quite well, after apparently mortal insult, but I'm left with the feeling that said insult was probably relatively minor - cutting in line or something equally petty - because he's just so unbalanced. There's a morbidly funny little line about a trowel in there, though. I think that's my favourite part.