Why Dumbledore believed Snape?

[anandamaz]

No: HPFGUIDX 165804

Among the few things that are still not quite clear in the books, one
of the biggest is Dumbledore's continuous belief in Snape.Was it only
because Dumbledore's tendency to believe people,as Barty Crouch jr.
said in book no.4:"it is so easy to manipulate decent people",or there
is yet some reason that is to be revealed.
                        Dumbledore was the only person among the
teachers who didn't loved him.One may say that the reason behind that
was their first meeting, where he saw every sign of evilness in
Voldemort.But remember,Voldemort never demonstrate his evil nature in
his company during his time at Hogwarts and Dumbledore also knew Snape
was a dark eater.Snape was the main culprit of he murder of Harry's
parents after Voldemort @ Wormtail.Is it that easy to convince a
intelligent person like Dumbledore by saying sorry ?
           Although there is much time left till the end(??),we may
still get our answer.Will a plotmaker like JKR leave that side weak?
Remember,we finally had our answer of the question:'why Voldemort
wanted to kill Harry as a kid'finally in the 5th book.So,hope for the
best and please let me know your thoughts about it

anandamaz