You're listening to the inquiry on the BBC World Service with me,

Helena Merriman. Each week we bring you four expert witnesses,

answering one pressing question from the news. It's November 2016.

Iraqi security forces have surrounded

Mosul, Iraq's second largest city, and are fighting the Islamic State Group for control.

House by house, street by street, they're crushing the militants.

Meanwhile, away from the front line,

thousands are trying to escape. No food, no water,

the muscle, debt.

They weave their way through the streets

and just as they think they've made it, one final hurdle.

A checkpoint manned by intelligence officials, they're on the lookout for members of IS. In their hands, not

guns, but laptops containing names of tens of thousands of suspected fighters.

Give one name, you make it through.

Give another, you're thrown into a van.

And so as one battle ends, another begins, the fight to bring those who fought for IS to justice.

Now they've lost the cities they once ruled, we want to know where they've gone.

So this week we're asking what's happening to IS fighters now. Part 1, the courtroom.

I spent many,

I spent many, many long nights in tents with families who had fled their homes talking

about really the horrors of life under ISIS.

Our first expert witness, Belkis Villa, the senior Iraq researcher for Human Rights Watch.

...