Dumbledores lack of surprise + my point !

[JoAnna]

No: HPFGUIDX 93924

Inge wrote:
> 
> Ok - so how DID Dumbledore know anything about Lily's sacrifice at 
> that time? Harry was a little more than a year old and the only 
> person to tell what had happened at his home that night. Not a 
chance.
> Alas! Someone else must have been in the house to witness what 
> happened and told Dumbledore that Lily actually gave her life for 
> Harry. Who? 
> And so, Dumbledore must have lied to Minerva when he told her that 
he 
> didn't know how Harry had survived the attack.

I think that someone did either witness or overhear Voldemort's 
confrontation with Lily, who then reported it to Dumbledore.  My 
guess is that Peter Pettigrew accompanied LV to the Potters that 
night, witnessed what happened, and fled when the curse rebounded 
onto LV.  Perhaps he saw Dumbledore shortly after and told him a 
different version of what had happened in order to throw suspicion 
off of him and onto Sirius.  I guess he told DD that Sirius had 
shown up at the Potters with LV, and all that had happened 
thereafter.  Then, later, when Sirius was about to confront 
Pettigrew, Pettigrew put his "escape plan" into action to further 
throw suspicion on Sirius and enabling him to make his escape.

As for what Dumbledore told McGonagall - my guess is that Dumbledore 
merely had a hunch or a guess about what had saved Harry, no 
concrete answers, and he didn't want to give McGonagall any 
information that might not be right until he had tested his theory. 
No doubt his guess wasn't confirmed until Petunia read the letter 
that DD left with Harry and accepted Harry into her home, sealing 
the charm and proving DD's hypothesis correct.

- JoAnna