Inside Branch 215, between torture sessions, Omar was forced to number and tag dead bodies. Hundreds of those bodies ended up at a hospital known as 601, where they were photographed by a military police officer known as Caesar, who later escaped Syria with more than 55,000 photographs the FBI has verified as evidence of Assad’s mass atrocities.

That evidence forms the basis of the Caesar exhibit at the U.S. Holocaust Memorial Museum in Washington. The State Department’s former war crimes ambassador, Stephen Rapp, has said this evidence is the strongest since the Nuremberg trials — and that Assad’s “machinery of death” is the worst since the Nazis.

Caesar testified before a House committee in 2015. Congress passed a sanctions bill, named after Caesar, just last month. His photographs have been shown around the world. Yet years later, Branch 215 is still churning out dead bodies. Assad’s prisons are just one component of the regime’s war crimes, which include starving cities, bombing hospitals and using chemical weapons, on its way to killing an estimated half-million innocent people.