old, old bones

There's a fine line between doing what's best for the greater good, and doing what's best for your own self interests. Aviens parents most likely knew that, and most likely, simply, disregarded it altogether. But unfortunately in the wake of that decision was left a boy who never got that opportunity— and struggles quite badly with understanding not only the innermost workings of right and wrong; things like morals and all of that, but even moreso with understanding reactions and emotional responses from those around him, especially when they're at him.

The things he does are for his own self interest, and in his eyes, that is just enough. Now, that doesn't sit very well through your school-years, as you can imagine. While growing children can and inevitably will be selfish, the extremities of his hunger and violence went far beyond that; and garnered quite the anger from students and staff alike, leaving him with the bare minimum of educational support outside what he pieced together himself—but at least it made him pretty good at dissecting things on his own.

And, after all of that, he's found he much prefers to keep most things to himself anyways. He doesn't understand the details or how's and why's, but all of this time seems to have only taught him that, whatever the whole mess even is, it has never does him any good to talk about it.

the night-life

And, regardless what he thinks, late in the middle of the night when he tries to sleep but can't stop tossing and turning; he can't really give up the whole ordeal. Nor can he really explain it— his explainations never warrented much understanding or change of perspective to anyone before, and his parents never seemed to try to do it themselves. Why should he, and why should he bother trying again? It only makes things worse. So he keeps the killings to himself, and feigns innocence when that aforementioned detective vents about un-named victims of ongoing cases, being careful not to let information out that she shouldn't be, but admitting how she can't understand the barely-present evidence or the extremity of the case.

gluttony's right-hand hound

Being undead isn't as simple as being a ghoul, or a zombie. He actually stems from one of the Sins; in this case, Gluttony in particular! Although, when boiled down to his most basic self, he is technically just a really impervious zombie. Death doesn't meet him readily, and, from his perspective, seems to have quite the disdain for him as it never seems to fully claim him, no matter the circumstances of his death. His worst consequence only seems to be the leftover scars and slow recoveries for his worse-off injuries.. But, it seems that being so closely and immediately below Gluttony in terms of "respect" from the Sin, or something like that, makes his case quite extreme..? Something like that, he guesses.