Dumbledore's suspicions of Moody, was The Problem with Lupin

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No: HPFGUIDX 97519

> > As I've said before, I do think that bits and pieces of 
> evidence--all of it presumably reported to him by others, 
> including Snape and the portraits--created suspicions in DD's 
> mind long before the Tri-Wizard Tournament. 

I don't know about "long before the Tri-Wizard Tournament", but he
would have almost certainly known by the start of Spring term. That
it, if he was given all the information that even Harry got.

1. As soon as Harry's name came out of the goblet Dumbledore knew that
Voldemort had an agent in place and was running some kind of rig under
the cover of the Tournement.

2. We don't know how widely the fact that Voldemort had "marked" his
followers was known. That's the kind of information Crouch Sr. would
have supressed as a security measure. The real Moody, as a working
Auror MAY have known of it. HOWEVER

3. The fact that he *taunted* Snape about it on the *very same night*
he raided the boomslang skin stores would have given Albus all of the
pieces necessary to draw the right conclusion. 

Namely: 
Raid on ingredient essential for Polyjuice potion
Moody's hip flask
reference to Dark Mark
Presence of a DE agent at Hogwarts

Would have made it pretty clear that "Moody" was almost certainly
their man. The identity of the person impersonating Moody might have
been uncertain for a bit longer. But Barty Crouch Sr's raving would
have been enough to bring Winky into it. Something clarly was going on
at the Crouch household, and she had been a member of it for a long time.