PHNOM PENH, Cambodia -- The fields of Choeung Ek on the outskirts of the Cambodian capital, Phnom Penh, carry a dark secret.

Across the baked earth scraps of cloth and human bone poke through the soil and are slowly bleached white by the harsh tropical sun.

In the corner of the field stands a tree -- tall, flourishing and peaceful now. A fading sign next to it, accompanied by a rudimentary painting, betrays its terrible past.

Against its trunk the heads of babies were smashed by young men brainwashed into believing their actions would free Cambodia from colonial imperialism.