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

[justcarol67]

No: HPFGUIDX 93969

Sue asked: 
<snip> Why did the Lestranges, Crouch and ? go after the Longbottoms?

Carol:  
It was Barty Crouch, Jr., and three Lestranges: Bellatrix; her
husband, Rodolphus; and his brother, Rabastan who Crucio'd the
Longbottoms. (Maybe we should call them BBRR or BRRB?) Sirius
identifies the third man somewhere in OoP--I think it's in "The Noble
House of Black" chapter. I'm still wondering why Rabastan is in the
story. Maybe he's part of the contrasting brothers motif? (I very much
doubt that he'll be "the good ex-Slytherin.")

Sue wrote:
<snip> Peter knew why Voldemort wanted the Potters and he knew there
was another couple who could have fulfilled the profecy. He sent that
horrible group to the Longbottoms to buy himself time to escape.


P.S. Although Wormtail may well have informed LV that the Longbottoms
as well as the Potters fit the Prophecy, he couldn't have been the one
who sent BRRB after the Longbottoms. He was already supposedly
"murdered" by Sirius (and apparently considered a traitor by Bellatrix
and Co. because of the backfired AK). The torture of the Longbottoms
occurred somewhat later, after most of the DEs were caught and people
were starting to feel safe.

Carol, who thought this was going to be a one-sentence post!