With what example can a teacher illustrate to his students that the ends do not justify the means of an act?

Question

my father teaches theology at my catholic high school... tomorrow he wants to give a good example illustrating that good intentions never justify an evil act... give us some ideas of a parable/fable/real life example... ten points to the answer that will most easily be presented to a high school religion class ^_^

Answer 1

http://www.goenglish.com/TheEndsJustifyT...

http://www.halexandria.org/dward818.htm

Hope this helps.  Seems like the second site has a better example.