Shot Dead
There were 23 prisoners who attempted escape and got returned to their cells, but some suffered a worse fate. Six of them had to be shot dead while trying to get free. The guards didn’t show mercy, and shooting them was best so that they couldn’t get off the island.
Drowned
Five prisoners actually got to the waters, but they drowned. There were few options, and swimming was the best choice. No one knows if they were simply poor swimmers or succumbed to the cold water, but they weren’t seen ever again. The four who succeeded dealt with that reality.