JKR's FAQ - Sirius (spoilers)

[dumbledore11214]

No: HPFGUIDX 114831


> Hannah:

 DD does say it.  Once when he says 'it is my fault Sirius 
> *died*' (p727 OotP UK Hardback) (emphasis mine), once when Phineas 
> Nigellus asks if Sirius is dead, and DD says 'yes' (p728 OotP UK 
> hardback).  He also talks about Sirius in the past tense 
throughout 
> this scene.  Pretty unequivocal in my mind.  But then I'm sure 
some 
> people will argue DD is wrong/ lying, which is of course possible.



Alla:

Not lying , Hanna, but keeping the truth from Harry. :o)

Especially since we have at least one occasion of him doing so.

Didn't JKR said that Dumbledore knows the true reason why he did not 
try to kill Voldie in MOM battle, but keeping it to himself.