They say mice get smarter, and therefore, if you want to catch them, you have to build a better mousetrap. It's natural evolution.
And with people being so well informed on how to avoid and defend themselves against being mugged, it stands to reason that eventually muggers would find a better "mug-trap," if you will. Knives, guns, and saying, "give me your money, or the goat gets it" in a low raspy menacing voice just doesn't cut it like it used to.
Enter the hand-held power saw ... for when you absolutely positively must have the person's wallet, keys, and any other belongings.
And if you don't believe me, ask Michael Steinberg who was attacked, on the subway, by a man with TWO power saws. He did not crack wise. He did not try to negotiate.
The Evolution of Mugging [BBC News]
How Do You Assist Against the Power Saw Attack? [NY1]