After receiving the news that the US army was advancing on Mittlebau-Dora, camp commander Richard Baer ordered that all prisoners be evacuated to other camps, leaving Brauny to oversee the evacuation. Within days, Brauny and 4,000 Jewish prisoners from Mittlebau-Dora and other nearby camps reached the town of Gardelegen, where the SS troops recruited auxiliary forces from the local civilian population to help guard the prisoners.
On April 13, Brauny directed the auxiliaries to herd 1,016 of the prisoners, most of them too old or sick to work, into a nearby barn. Brauny's men then barricaded the barn and set it on fire. When the prisoners attempted to dig their way out the guards shot them. US forces reached Gardelegen two days later, finding the charred remains of the victims.
In 1947 Brauny was arrested for war crimes and charged at the Dora Trial, alongside other officials at Mittlebau-Dora. He was sentenced to life imprisonment, dying of leukaemia three years into the sentence.