“We were not prepared for what we were going to see,” says Human Rights Watch researcher Hiba Zayadin, who recently visited one mass execution site turned mass grave in Syria, following the sudden fall of the authoritarian Assad family from power. More than 150,000 Syrians remain unaccounted for after being held in Assad’s prisons, and many are believed to be buried in mass graves. We speak to Zayadin about what’s been uncovered so far and the struggle to preserve evidence, particularly in the face of a new regime that has not prioritized tracking records of the Assad government’s crimes, and of Israel’s ongoing shelling of crucial sites. “Every minute that passes where there is inaction, where these documents, these sites are not being preserved, are not being secured, is just one more family possibly never knowing what happened to their loved ones,” she says.