What if Snape was at the Peter/Sirius showdown?

[pippin_999]

We've speculated that Snape might have been with Voldemort when he
went to kill James and Lily. We've speculated that he might have been at
the Graveyard in GoF. But I don't think I've ever seen anyone speculate
that Snape could have been present at the big showdown between Sirius
and Peter. If so, he could have been taken in like everyone else. But
he wouldn't be able to reveal that he'd been there without blowing
his cover. 


If Snape was actually there, it explains a lot about why he
didn't want to believe Sirius, and why Dumbledore was so convinced of
Sirius's guilt that he never questioned it until Sirius escaped. Even
if Dumbledore watched the scene through Snape's memories in the
Pensieve, it might not be possible to tell whose spell had made the
street blow up, given what we now know about non-verbal magic.
And unless you were looking for it, you might not even see Peter
turning into a rat.

It also sets up a very nice possible parallel with the Tower scene, where we
have another young wizard who would be very reluctant to think his
eyes had deceived him. 

It also adds another layer of meaning to Snape's question. "And does my evidence
count for nothing?" 

Thoughts?

Pippin