Who is Dumbledore?

[S Handel]

No: HPFGUIDX 78259

Hi,
I did search posts but couldn't find this.....If Dumbledore knows 
everything that is going on then how did he not know there were three 
unregistered animagi running around Hogwart?  Why did he not know 
that Moody was not Moody?  Why did he need Veritaserum when he did 
discover Barty/Moody?  Does he have selective knowledge the same way 
some people (especially kids) have selective hearing?  It is very 
confusing to me to really get a sense of who Dumbledore is and what 
his intentions are when one minute he already knows what is going on 
and what is going to happen and the next minute he is clueless.  He 
also knew of the DA but didn't know they called 
themselves "Dumbledore's Army"?  
Susan who is on an emotional rollercoaster when it comes to 
Dumbledore.