Dumbledore Does Lie - Sort Of

[pippin_999]

No: HPFGUIDX 159706

Just_Carol:
> Carol, who thinks that Dumbledore must have had good reason for
> believing that he had matters under control (and to trust Snape) but
> wishes that he had not chosen to fly to the astronomy tower after he
> returned from the cave
>
Pippin:
"Every secret passageway out of the school was covered. We knew
nobody could fly in. There were powerful enchantments on every
entrance into the castle. I still don't know how the Death Eaters could
possibly have entered..." -McGonagall, HBP ch 29

Notice that they  knew the enchantments hadn't been breached. 
They must therefore have a way of  monitoring the defences.
Dumbledore would have expected to know if the whooping meant
Draco had done something to enable the DE's to get in.

What  is it  Dumbledore should have done if he'd been listening 
to Harry? Dumbledore  could have searched the RoR's chamber
of hidden things as long as he liked and not found what Draco was
working on, and maybe he did.  Trelawney's tale could have
shortened the search considerably if she could have pointed out 
where the voice came from. I am not saying it is Harry's fault,
just pointing out that AFAWK, there was nothing in Harry's report
that would have alerted Dumbledore to anything that he didn't
already know.

There was nothing more to be done, short of confronting Draco
himself. But Dumbledore believed that it was Voldemort's plan that
he, Dumbledore, should be the instrument of Draco's death, and
that if this plan failed, Voldemort would kill Draco himself. DD had
all the more reason to believe this if Snape had revealed the third
portion of the vow, because the only thing it protects Draco from
is Dumbledore -- it doesn't do anything to stop Voldemort from
trying to kill Draco, it just removes one possible means of doing
the job.

Thus, to confront  Draco without the means to protect him would 
be to do to Draco what Snape did to Harry when he revealed the 
prophecy to Voldemort: mark an innocent child for death on the 
basis that he is to be feared.

Pippin