What gave people the idea Sirius was Voldemort's No. 2?

[banjoken at optonline.net]

No: HPFGUIDX 23970

> If the general population had learned that Sirius was NOT the 
>Secret Keeper and that Pettigrew was, they would not assume 
>Pettigrew was 

It's important to remember here that the general population didn't 
even know there was a secret keeper. If I recall Fudge's conversation 
correctly, nobody knew about the Potters going into hiding, or having 
the charm put on them. All they average wizard knows is that the day 
after the Potters were killed, Pettigrew cornered Black, and Black 
destroyed the whole block and killed 13 muggles. If this is all they 
knew, it would seem pretty reasonable to assume that Black was 
working for Voldemort.