Why did Sirius trust Pettigrew? WAS: Snape investigating Potters' Betrayal

[pippin_999]

No: HPFGUIDX 186574


> 
> Carol responds:
> I agree that we need some explanation for why the Aurors didn't just examine the arms of suspected Death Eaters and round them up,

Pippin:
We have it. Sirius didn't know about the Dark Mark, so it's pretty obvious that during the first war it was known only to loyal Death Eaters, Severus Snape and Dumbledore. The Aurors probably never got close enough to any marked Death Eaters to discover it. Karkaroff doesn't seem to have revealed the existence of the Dark Mark at his trial though he obviously knew about it. Apparently it had faded so much that it wasn't recognizable any longer.

Snape, Rookwood and Peter Pettigrew never drew any  suspicion on themselves at all while Voldemort was active. AFAWK, Lucius and his cronies only became suspects after Voldemort's fall, when the Death Eaters were in disarray and victims were less afraid to come forward. But even then, they couldn't have pleaded Imperius if most people, unlike Arthur and Dumbledore,could never  bring themselves to believe that such people would have served Voldemort willingly. 

Voldemort picked people who would never be suspected for his marked DE's -- that was the brilliance of it. 
 
I'm sure Snape told Dumbledore about the Dark Mark. But it's the usual dilemma in espionage: the more secret the information, the harder it is to use without compromising its source. If  Dumbledore started finding excuses to examine people's arms, the spy would surely report that to Voldemort, perhaps as his last act before being captured.  Voldemort would then deduce that Snape had revealed the secret. Dumbledore couldn't risk that.

Pippin