Two mass graves have been located near Damascus. They are believed to hold thousands of bodies of Syrians who were killed in detention centers run by President Bashar al-Assad’s forces.

Interviews The Times conducted with four Syrian men who worked at or near secret mass graves led to an examination of satellite images. Those clues revealed the locations of two sites. Each one holds thousands of bodies, according to the men who worked there.

The graves could contain powerful evidence of war crimes committed by al-Assad’s forces, including systematic torture.

Throughout Syria’s 11-year civil war, more than 144,000 people disappeared into government detention centers. Many of them are presumed dead. The U.S. Treasury Department said last year that at least 14,000 had been tortured to death, but the actual number is almost certainly much higher. Counting and identifying the bodies is unlikely to happen with al-Assad in power. Russia continues to support him, and he and his senior officials have never been held accountable for wartime atrocities