Hidden Meanings in Amnesia? (SPOILERS)

[Commando Peach]

I interpreted it as Daniel carrying the shadow into the orb chamber and destroying the only thing that lets Alexander control it and keep it at bay, namely, the orb(s?). It kills Alexander, and I guess it takes that as sacrifice enough to satiate it, and then Daniel walks free.

I think the only reason it killed Alexander instead of Daniel is because the shadow is just sort of "following" him and killing those around him (like those professors he spoke with). I don't understand it full either, though.