Abraham's Dilemma

Abraham, a young politician, lives in a large city. One day, a group of terrorists steals a nuclear bomb and, to prove that politicians are immoral, they give a choice to Abraham: either he will torture his mother to death or they will destroy the city.

Now, of course, the question is what Abraham should do? (The answer that terrorists can't be trusted to keep promises is not the solution.) Torture his mother to death or let kill some millions of innocent people (perhaps including his and the mother)?

There is one more problem to be solved, the question of responsibility. If Abraham tortures his mother, is he responsible for her death? "Of course, he did it!" you would probably say. But has he a free choice? Indeed it is not his will to kill her.
And, further, if he rejects to kill her, is he responsible for the death of the city's citizens? One one hand, it isn't he who has fired the bomb, but, on the other hand, thanks to his decision not to kill his mother, the people died.