4 criminals

The 4 criminals are lined up on some steps. They areall facing in the same direction. A wall separates the fourth man from the other three. So to summarize:
Man 1 can see men 2 and 3.
Man 2 can see man 3.
Man 3 can see none of the others.
Man 4 can see none of the others.
The criminals are wearing hats. They are told that there are two white hats and two black hats. The men initially don’t know what color hat they are wearing. They are told to shout out the color of the hat that they are wearing as soon as they know for certain what color it is.

They are not allowed to turn round or move.
They are not allowed to talk to each other.
They are not allowed to take their hats off.
Who is the first person to shout out and why?