One of the more chilling headlines I've read so far in my life. The article goes on to say:

UN officials say as many as 12,000 bodies could be buried across 202 sites

Btw killing people en masse and dumping their bodies in mass graves is in fact a sunnah:

Then they [Banu Qurayza] surrendered, and the apostle confined them in Medina... Then the apostle went out to the market of Medina (which is still its market today) and dug trenches in it. Then he sent for them and struck off their heads in those trenches as they were brought out to him in batches... There were 600 or 700 in all, though some put the figure as high as 800 or 900. Ibn Ishaq's Sirat Rasul Allah - The Life of Muhammad - Translated by Alfred Guillaume - p. 464