Why did the SS flee the concentration camp? When , was Eliezer Wiesel finally freed?

On April 10, the 20,000 prisoners at Buchenwald are to be evacuated and the camp blown up. A siren alert occurs, however, and the evacuation is postponed to the next day. Nobody had eaten anything for six days. The next morning the resistance movement suddenly battles the SS in the assembly place. The SS flees, and resistance takes charge of the camp. At six in the evening, the first American tank arrives at Buchenwald.