Syria's brutal civil war rekindled suddenly after 13 years, with rebels staging a shock offensive that forced long-time dictator Bashar al-Assad to flee to Russia.

Najem al-Moussa was delighted when news of Syrian President Bashar al-Assad's overthrow first beamed from the television in his tiny Athens apartment.

NBC News' Richard Engel reports from inside one of Syria's most notorious prisons, Saydnaya military prison nicknamed "the human slaughterhouse." Thousands of people in Syria have rushed to the country's prisons after the fall of the Assad regime searching for any trace of loved ones they feared had disappeared into their unseen depths.