Voldemort to Vapormort - How Did They Know?

[gelite67]

No: HPFGUIDX 150407

I've always believed that someone else was present at GH on the night 
of Voldemort's downfall.  Otherwise, how would anyone besides Harry 
(who couldn't remember) have known, prior to any admission by 
Voldemort, that Voldemort's powers had been broken or that Voldemort 
tried to perform the AK spell on Harry that rebounded on him?  It seems 
to me that anyone happening upon the scene afterward would think the 
perpetrator simply caused all the damage and then left.  Why would 
anyone assume it was an AK spell gone awry if, to the best of wizard 
knowledge at that time, there was no way to block an AK spell and make 
it go awry?

For that matter, how did DD know in SS that Voldemort was the one who , 
in fact, killed James and Lily and tried to kill Harry?  Obviously, 
this is confirmed later, but how did DD know at the time unless there 
was a witness who told him? (Snape, IMO)  It's hard for me to belive 
that Voldemort would have gone there alone -- he would have wanted at 
least one DE there to impress, wouldn't he?  Bragging rights and all 
that.

I know that magic leaves traces, but enough to figure out what spells 
were cast, which were unsuccessful, and what the consequence of any 
failed spells were?

I guess I've always assumed that DD never saw Harry until Hagrid 
brought him to the Dursleys.  Is is possible that DD saw Harry before 
then and extracted Harry's memories of the events?

Is there any other explanation for how DD knew what happened that night 
other than hearing/seeing the story from a witness?  

Angie