It really annoys me ...

[justcarol67]

No: HPFGUIDX 163829

Jeremiah wrote:
> 
> Well, I would think that you can only find out the previous spell
cast by a wand but not a long line of them, so if you were going to
try to hide something you can cast another spell and be safe. (of
course, if Sirus is accused of AK'ing Pettigrew and then they find
something like Alohamora then it would look suspicious, woudn't it?)
> 
> I think this is the reason because it is called "Priori Incantatum"
 is singular. We might be confusing it with "Prioir Incantata" wich is
plural and is what happened with LV and Harry. <snip>So, with any
other wizard I would think you can only go one spell back but with
Harry and Voldemort you can go back all the way to the very beginning.

Carol responds:

Erm, no. The spell that Amos diggory casts on Harry's wand to
determine the last spell cast is Prior Incantato, singular (GoF Am.
ed. 136). The effect of the brother wands in conflict with each other
is Priori Incantatem (GoF, title of chapter 34). It seems perfectly
possible to cast a Priori Incantatem spell to discover an indefinite
number of spells cast by the wand. I wonder, in fact, if the DEs
periodically "clean" their wands using this spell (Of course, the
presence of Prior Incantato/Priori Incantatem would in itself be
suspicious, but it would remove evidence of any darker spells.) So,
IMO, the Aurors would not have examined the wand because they would
have destroyed the evidence. However, Barty Crouch Sr. could have used
Priori Incantatem to determine whether that wand had cast the spell
that blew up the street (they would know what the spell was either
from its effects or from the MoM spell detector that told them such a
spell had been cast in the first place). The absence of either that
spell or some form of Priori Incantatem would be strong evidence, if
not proof, that that wand had not been used to blow up the street, but
it would not be proof of who had used the wand (see GoF, where Winky
is accused of casting the Dark Mark because the "guilty wand" is in
her possession). 

Granted, Barty Sr. could and should have used the spell to determine
Black's guilt. Why didn't he? Because, IMO, it was an open-and-shut
case. The witnesses had heard Peter Pettigrew say, "James and Lily,
Sirius. How could you?" They had seen Sirius Black raise his wand and
perhaps cast some spell; otherwise, they would not have claimed that
*he* had blown up the street. They had *not* seen Pettigrew raise his
wand; it was behind his back. They had seen the street blow up,
killing twelve Muggles. They had seen Pettigrew vanish, with nothing
left but a bloody cloak and a finger. (Fudge claims that there were
other "fragments" though that seems unlikely; maybe they were bits of
a Muggle?) The Aurors arrived to find an armed and maniacally laughing
Sirius Black, a Pettigrew who has apparently been blown to bits, and a
number of Muggle witnesses all telling the same story. And then
Dumbledore tells Crouch that Black was the Potters' Secret Keeper. Why
would Crouch or anyone else think to examine Black's wand--or the
"dead" Pettigrew's--to determine which of them had cast the spell? If
Black had behaved differently (personally, I think he was temporarily
insane from grief and rage), if he had calmly stated the facts, even
admitting to being an illegal Animagus as evidence that PP was one,
too, and offered his wand as evidence or suggested that they check
Pettigrew's, he could have been proven innocent (though he'd probably
have had a short term in Azkaban for being an unregistered Animagus).
But he must have thought that the evidence against him was
overwhelming. Or perhaps, having lost James and Lily (and denied
custody of Harry) and failed to bring PP to justice, he just gave up,
laughing madly and bitterly at the irony of fate. He could have asked
to talk to Dumbledore or to Lupin. He did nothing. I'm not blaming
him. Under the circumstances, I'd have given up, too. (Okay, I
wouldn't have gone running after Pettigrew to seek revenge, but aside
from that . . . .) I'm just trying to explain why I think that Crouch
et al. didn't use Priori Incantatem on Black's wand. They weren't
looking for a scapegoat. They were certain that they had the right man. 

Carol, noting that Black could have averted the whole fiasco by going
to Dumbledore rather than seeking vigilante justice against Pettigrew