Yes, I agree with mayfic's comment, too! The whole framework of DN is essentially Raito's spiral, the curve of his actions starting out fairly small and manageable but as the ante is upped (or he inadvertently "raises" by killing off the FBI agents) it eventually gets too large for him to handle, he stretches himself too thin and loses control.

I remember a doujin in which Raito dies of old age and ends up in the shinigami realm where he's told his punishment will be to "relive" the death of every person he'd killed. At first he's terrified, but then he realizes that this punishment at least give him some time to "live" so he decides to go and make an offer to the shinigami king to help revive the realm or some such. Despite my misgivings about Raito, I can totally see this happening (him trying to match wits the shinigami "old man" and maybe even win him over). I was amused by it, though I suspect the (human) world he left behind was pretty much "unliveable" at that point.