PoA - Snape knew?

[ginny343]

No: HPFGUIDX 143349

I had a thought this morning and although I have not thought it 
completely through, I decided to post it.

We know from PoA that the DEs knew that Peter was a spy.  

"You've been hiding from Voldemort's old supporters . . . Sounds like 
they think the double-crosser double-crossed them . . . " (Am. ver. p. 
368)

So, he was probably part of the /circle/ (literally) of supporters 
that Voldemort would call to him (like in the graveyard).  There was a 
place for Snape too (the one he thought had left him forever).  So 
that means, like all the other DEs (loyal or not), Snape knew Peter 
was the spy.

That given, I am a little confused about why Sirius was believed to be 
a spy.  Did they think there was two spies working on the same thing?  
Did Snape think Sirius went after Peter to kill him because Peter had 
caused the downfall of Voldemort? Or did Snape, like the others, think 
that it was Peter who went after Sirius (out of grief?) and got 
killed?  Seems to me that Snape must have known that Sirius was 
innocent.  Or at the very least, Snape knew Peter had been the 
betrayer, not Sirius.  I can believe that Snape thought Sirius was 
guilty of killing the muggles and Peter.  But Snape, as a DE, must 
have known Peter was the one to give information to Voldemort.  

Although I am really hoping to see a turn for the good in Snape in the 
7th book, I am a little disappointed to think that Snape knew about 
Peter, and yet the teachers in the school believed Peter to be 
innocent.  Did Snape tell DD otherwise and DD kept this information to 
himself?  Or did Snape not share this information because he wanted 
Sirius to be killed/dementor-kissed?  If Snape withheld this 
information, surely DD figured out Snape knew about Peter . . . And 
even if Snape told DD and DD kept the info to himself . . . after all 
of what happened in PoA, Snape should have told the minister that 
Black was not the one who got James and Lily killed.  Why didn't he?


Any ideas?   

Ginny343