As much as I'd hate to do it, I would let them all die. To save them would be to cause, rather than allow a death. For that I would suffer the most guilt, and I might even end up in jail. My choice would also prevent a tremendous burden on the prisoners; were they to survive, they would hold themselves partly responsible for the one person's death.
EDIT: That's also how I would respond to the second situation. There's no difference between them for me; the wording changes nothing.