riddle (sorry for bad english)

The group of pirates is noted that exactly three pirates regularly steal the booty.
After they were caught in the act They decided that they, rather than execute, provides another chance.
They lined them up in a column so that last see the other two, the middle one see only the first, and the first not see anyone, and they put a black or white hat.
They said they would leave them in life if at least one guesses the color of his hat, and that they all execute the same moment when someone says the wrong color of his hat, he gets executed.
They asked them in order, starting from the last, which is looked after hats the remaining two,
Then they asked the pirates in the middle, which is also, after he looked at the hat pirates Up ahead, he concluded that he could not figure out the color of his hat, and said he did not know.
However, to the surprise of all present, a pirate who was the first in the column, hearing responses remaining two said it now knows the color of his hat.
What color was his hat (give an explanation too) if everyone knows that the whole group of pirates has only three black and two white hats?