Hat Riddle I

There's a serial killer who kidnaps 3 men. The killer buries the men in the ground up to their necks so that they can't move around. The men are buried in a position so that they're all facing the same direction and also one behind another, but not directly behind, as shown:

Person C can see person B and A.
Person B can only see person A.
Person A can't see any of the other two.
The killer can see all of them but none of them can see the killer.

The killer then takes out 4 hats.
2 Hats are black.
2 Hats are white.

The killer puts a hat on each of the person's head and then the last hat on himself. He then tells the three guys that if any ONE of them can correctly guess the color of his OWN hat, they will ALL be set free. However, the FIRST word out of ANY of their mouths, has to be the correct color of his own hat. If not, all of them will die. Because of this, the 3 guys can not collaborate or discuss how to solve this riddle.

There is a 100% sure way to figure out the correct color but how do they do it?