"Of course it's my fault. There's no one else here who could be responsible for anything."

The first time this sentence appears in HPMoR is in the italic text that begins Chapter 2:

"Of course it was my fault. There's no one else here who could be responsible for anything."

I'll assume the difference between "it's" and "it was" isn't significant. I'm inclined to refocus my attention now on the italic text that begins Chapter 1:

Beneath the moonlight glints a tiny fragment of silver, a fraction of a line...

(black robes, falling)

...blood spills out in litres, and someone screams a word.

I didn't know what to make of this when I first read it, and I still don't. Does this describe an event that has already happened? It's not Hermione's death, since that didn't happen in the moonlight.