“The further development of this example involves the case, where the fat man is, in fact, the villain who put these five people in peril. In this instance, pushing the villain to his death, especially to save five innocent people, seems not just moral, but, to some, also just and even an imperative. This is essentially related to another famous thought experiment, known as ticking time bomb scenario, which forces one to choose between two morally questionable acts. Several papers argue that ticking time bomb scenario is a mere variation of the trolley problem.”
http://en.wikipedia.org/wiki/Trolley_problem

The further development of this example involves the case, where the fat man is, in fact, the villain who put these five people in peril. In this instance, pushing the villain to his death, especially to save five innocent people, seems not just moral, but, to some, also just and even an imperative. This is essentially related to another famous thought experiment, known as ticking time bomb scenario, which forces one to choose between two morally questionable acts. Several papers argue that ticking time bomb scenario is a mere variation of the trolley problem.”

http://en.wikipedia.org/wiki/Trolley_problem