In just over a week, Syrian rebel forces seized much of Syria’s northwest. First, the rebels captured Syria’s largest city, Aleppo, then Hama and Homs. On Sunday, they entered Syria’s capital, Damascus, taking the city without a fight as government forces fled.

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.