On January 8, 1979, two Vietnamese photojournalists wandered through the south side of Phnom Penh.

The capital was quiet, almost silent.

The pair were looking for the source of a terrible smell, the smell of rotting flesh.

Elsewhere across the city, Vietnamese troops patrolled empty streets.

Following the scent, the pair came across a compound, fenced off with barbed wire.

It was an old school, concrete buildings,

beaming white against the sunlight. Patches of green grass and coconut trees broke

up different blocks of the compound. The two men entered one of the buildings.

What they saw were corpses, chained to beds by manacles.

Their throats cut.

In other rooms, whips, chains, handcuffs.

In each building's upper floor, they found a series of makeshift prison cells and what looked

like medieval torture devices.

The two journalists photographed what they saw and ran back to inform the Vietnamese soldiers.

What had happened here?

The Vietnamese army, which had invaded Phnom Penh a day earlier, soon put the pieces

together. This compound was the main torture center of the Khmer Rouge, which had ruled

Cambodia for the past four years. This facility was known as S-21. The S, writes historian David Chandler, stood for

Sala, or Hall, while 21 was the code number assigned to the word Sontabal, a Khmer term that

combined the words security and police. S-21 and Sontival were names for Democratic Campuchia's security police or special branch.

Before it had served as S-21, the compound had hosted a lycée and primary school, called Tulslang, and that was the name that would become shorthand for the entire torture complex.

As we walked through the place during our own research in Cambodia, it was impossible not to notice the contrast between the design of the area, the classrooms, the sunny courtyards,

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