What did Snape know, and When did he know it?

[Mike]

No: HPFGUIDX 169376

Mike:
I was going to respond point by point, but that didn't work so well 
last time. So instead, let me lay out my theoretical timeline and you 
all can point out where I'm off base. :)

1) Peter Pettigrew starts spying for Voldemort.
There are a fair few true DEs that know that Severus Snape is spying 
for Voldemort. I gotta believe that although Voldie would hold 
Peter's allegiance close to the vest, he would tell someone. 
Pettigrew would have a handler, a middleman who took Peter's info to 
LV. And he probably told more than just that one. He wouldn't want to 
have to handle Peter personally all the time.

2) Dumbledore suggests the Fidelius to the Potters. They tell DD they 
are going to use Black, then switch at the last minute to Pettigrew.
I would think that DD would have told Snape about the Fidelius and 
that Black was going to be the SK. If for no other reason than Snape 
would have the same plausible deniability that he had with Bella in 
Spinner's End. To wit: I can't tell you where the Potters are, they 
are under the Fidelius Charm. And why would DD hide his understanding 
that Black was the SK? Besides, it seems to have become a known fact.

In quick order,
3) PP gives up the Potters. LV goes bye-bye.
4) Sirius tracks down PP and we get 12 dead Muggles and a missing and 
presumed dead PP.
5) Sirius is accused of the murders of all 13, thrown into Azkaban 
without trial. 
6) Sometime in here DD gives testimony that Sirius was the Potter's 
SK. To whom, we aren't told, but presumedly to Crouch Sr.
This is about where we are in PS/SS when we meet DD, MM, and Hagrid.

7) The in-the-know DEs start spreading it around that PP was the 
Potter's SK and led LV to the Potters, whereupon he vanished.
As I explained previously, these few in-the-know DEs don't want to 
take the fall for LV's demise. So they start releasing to their 
bretheren who the spy was. And why not, they all believe that PP is 
dead. Who better to pin the screw-up on than the dead spy? And why 
keep the dead, screw-up spy's name a secret, that only makes the 
others suspicious that one of them was the screw-up, if the others 
don't get a plausible name.

8) Snape learns this info about PP in due course and reports it to 
Dumbledore.
Dumbledore has a dilemna. He now knows that Sirius wasn't the 
Potter's SK, but he's already given testimony to the contrary. His 
information comes from his double agent, so he doesn't necessarily 
want to come forward with it. Without LV around, who knows how the 
rest of the DEs may respond to finding out Snape told DD this info. 
And the DEs would obviously suspect Snape as he is currently employed 
by DD. Besides all this, DD has no proof and no knowledge that Black 
wasn't responsible for 13 murders (well 12 and change) and for all we 
know, this is the primary charge that got Sirius thrown into Azkaban.

This doesn't look like a fight DD can win, and he would be putting 
his double agent in jeopardy if he tries. He gives it up as a bad job 
and consoles himself in the knowledge that Sirius screwed up once too 
often and it finally caught up with him.

9) Snape knows the true identity of the Potter's SK.
(Scenario #1)
But Snape also knew the Potters told DD they were going to use Black. 
Why would they switch to PP? Couldn't Snape believe the same thing 
that Sirius tells Harry in the Shreiking Shack? That is, that the 
idiot Black convinced the Potters to switch to the traitor Pettigrew. 
Who else besides the arrogant Black would be so convinced in the 
brilliance of a stupid plan like that? So Snape still blames Black 
for the Potters demise and, maybe worse, it was because of Black's 
arrogance.

(Scenario #2)
There is second possible explanation for Snape's perception. He 
believed that Black was in cahoots with Pettigrew. He convinces 
himself that Sirius had decided to return to his Black roots and was 
going to join up with the Dark side. And that Black went after 
Pettigrew for the same reasons that any other DE would have gone 
after Pettigrew, he led LV to his demise. Nobody understood what 
happened that night at Godric's Hollow. Could some DEs have believed 
that Pettigrew "double-crossed" LV and that he was the proximate 
reason for LV's downfall? Snape could have credited Black with this 
same motivation if he believed that Black was switching sides.

I don't find the second scenario plausible. But apparently the WW 
didn't have too much of a problem with it. <shrug> Normally, I would 
credit Snape with more sense than to believe this hooey. But, if 
Snape is blinded by his hatred of Black, I can see him accepting this 
explanation. It's like Magpie said, of course he wanted the traitor 
to be Black.

Either of these two scenarios makes what Snape said in the Shack 
about "died like your father - too arrogant to believe you might be 
mistaken in Black", a plausible utterance.

10) Snape believes that Lupin is helping Black in PoA.
If Snape is blinded by his hatred of Black into believing that Black 
was the reason for the Potters demise, it's not too big of a leap to 
believe that Lupin has also fallen under Black's spell. This is my 
biggest complaint with Snape. He has convinced himself that Black has 
this hold over Lupin because if his irrational hatred of Black. Not 
Snape's best moment, imo. Snape's bits of "evidence" here and there 
are totally outweighed with the preponderance of evidence to the 
contrary. The contrary evidence was there to see, but Snape didn't 
want to see it, imo.

11) Snape is convinced that Black is trying to kill Harry.
Snape could believe this under both of the above scenarios. First, he 
could believe that Azkaban addled Black's mind, not an unlikely 
outcome after 12 years with the Dementors. And in the second 
scenario, well that one has Black switching sides just like the rest 
of the WW believes. Again, why he believed Lupin was helping Black is 
a problem for me. And as Carol has pointed out (and Dumbledore said 
to Harry and Hermione) Black hasn't exactly acted rationally 
throughout the whole of PoA. We understand what was going on, now, 
but I wouldn't expect any of the characters to react to it in any 
other way than they did, including Snape.

12) Snape enters the Shack convinced of Black's guilt.
Given everything else that led up to this point, what else would 
Snape have believed? That doesn't mean that Snape's hatred is 
rational, making his false conviction partially his own fault. But, 
also remember, nobody has any evidence that Black didn't kill those 
13 people. So Black is still a criminal in the WW regardless of his 
status vis-a-vis the Potters. This makes Snape's attempt to capture 
Black perfectly plausible on the grounds of the 13 murders alone.

That said, I still have a problem with his treatment of Lupin. I see 
a lot of werewolf prejudice in the Shack. And Lupin's admission (that 
Snape heard) that he was weak and cowardly is not the same thing as 
admitting that he was helping Black. But that's the way some folks 
think Snape heard it. That sounds like rationalization to me, 
excusing Snape's bias against Lupin. 

Thanks for your indulgence.
Mike