OOP: Life Debt?

[Tom Wall]

No: HPFGUIDX 66949

Maggie B. wrote:
<snip earlier stuff>
Also, so much was going on in that room, how do we know that Sirius 
didn't, I don't know, step between Bellatrix and Harry as she 
yelled "Avada Kedavra"? That would make the life debt even more 
evident.

Tom replies:
I think we can be fairly certain that she didn't use Avada Kedavra 
because the color of the spell that hit him was red, and Avada 
Kedavra results in a green light. That, and the observation that 
Sirius didn't die when the spell hit him - his "eyes widened in 
shock." (OoP, Ch.35, 805, US edition) 

As we know from GoF (both when Crouch!Moody uses it on the spider, 
and when it's used later on Cedric) a successful Avada Kedavra 
immediately kills the recipient, leaving no signs of physical 
stress; the person simply drops dead. If Sirius' eyes widened, I'd 
say that he didn't immediately die from the spell. I think that he 
died because he accidentally fell through the veil, which appears to 
represent some kind of entrance to "death."

-Tom