sirius as animagus - why didn't the deatheaters know pre OOP?

[Berit Jakobsen]

No: HPFGUIDX 93824

princess laura wrote:

<snip>In Voldy War 1 we know that Wormtail was passing information to 
Voldy for a year before his fall.  Yet it is implied in OOP that the 
death eaters did not know this [about Sirius being an animagus] until 
after Voldy's resurrection. <snip> Wouldn't Peter have been passing 
this kind of info about the members of the Order?

Berit replies:

I believe Peter realised it would be smart to not tell everything... 
Like Lucius, Peter is a very *slippery friend*, and would want to 
cover his back and have an escape route should something go terribly 
wrong. An when it did, he could turn into a rat and no one would be 
any wiser as to his whereabouts (except Sirius who he believed was 
safely locked up in Azkaban). His rat-disguise was a safety measure. 
I believe he did not tell either Voldemort or his DE's about Sirius, 
James and himself being animagi because it was useful to keep that 
information to himself. He could of course have told Voldemort about 
Sirius and James and "forgotten" to tell about himself. But if it 
came out his former friends were animagi, don't you think Voldemort 
would have suspected Peter might be one too and force him to admit 
it? No, the safest thing was to keep the whole marauder-animagi a 
secret. I think Voldemort only learned about Peter's rat-form when he 
came to his rescue in the Albanian woods.

Berit
http://home.no.net/berjakob/snape.html