Hello and welcome to News Hour from the BBC World Service coming to you live from London with me, Sean Lay.

They are the silent witness of atrocity. Mass graves uncovered after a regime falls.

On Tuesday, after visiting sites close to Syria's capital, Damascus, Stephen Rapp, who led prosecutors for the

tribunals investigating war crimes in Rwanda and Sierra Leone, suggested that what he called

the organised killing by the state, we really haven't seen anything quite like this since the Nazis.

The Syrian Emergency Task Force, a humanitarian and activist organisation, estimates half a million bodies can be buried in mass graves in Syria.

Moaz Mustafa from the task forces back in the country after operating his group from the United States,

he told the BBC's Sarah Montague what they found out so far about Syria's mass graves.

We found out years ago back in 2021 about these mass graves because we talked to these

mass grave workers that work there. And what we know now is I was able to go to these

locations and not just see them on Google Earth, on satellite images as we had before,

but see them in person.

And there are hundreds of thousands of men, women, children, elderly in these mass graves.

And we know that because all of these different witnesses that worked on the mass graves

told us that every single week, twice a week, four big trailer trucks with at least 100 people each

and filled up these mass graves, that means that there is in Qatifa alone, at least conservative

estimate is 300,000, closer to 350,000 or more.

And there are more mass grave locations?

Yes, this one is the biggest.

There are other ones.

Our organization, certain emergency task force, have been able to identify working with

these key witnesses and mass grave workers, multiple sites, including Nijha, south of Damascus.

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