I don't think he ever looks like a serial killer, just... Serious, really... But yeah, smiles from him are rare, and even the times he has smiled have been either nervous/faked or kind of small smiles.
Am I the only one who thinks that's supposed to be Romano? Because if you ever rewatch that clip I swear to god he looks and sounds just like him. I imagine the anime did that and not the manga, though.