This is the Guardian.

Today, the first of a special two-part investigation,

about two ordinary people who find evidence of a war crime,

and then decide to go undercover to find the man responsible.

Before we start, a heads up.

This episode contains extremely graphic descriptions of violence.

If you're feeling in any way sensitive, especially with everything going on in the world at the moment,

you might want to save this and come back to it another time.

A few years ago, somewhere in the Syrian capital, Damascus,

a laptop broke down.

This particular laptop belonged to an office of a Syrian intelligence agency,

called Branch 227.

And hey, wherever you are, good IT support is hard to find.

So one of the commanders of this unit says,

I know a guy. He's a young recruit to a militia working with the Syrian army

and he's good with computers.

But what the commander didn't know was this young guy,

he was also filled with doubts.

Doubt that he's on the right side of this civil war that's been engulfing Syria since 2011,

whether he's doing the right thing, fighting on the side of the government.

And when he starts looking through the laptop, trying to fix it,

he says something, a video.

...