See Slate's complete coverage of the Gabrielle Giffords shooting and the arrest of Jared Lee Loughner.
Loughner's favorite book, according to news reports, fits with these troubled-guy tendencies and their associated pitfalls. It's not Beyond Good and Evil, but rather The Will to Power, the notorious compilation of Nietzsche's working notes (which Nietzsche's sister peddled, wrongly, as his great systematic work). The observations are longer-form in The Will to Power, but, like the "Epigrams and Interludes," they are too-easily separated from Nietzsche's other work. They have a tidy thematic organization that is largely his sister's. This scheme is helpful to the scholar who knows his other books. It's also helpful to the troubled young man obsessed with one thing in particular. In Loughner's case, this one thing was apparently nihilism, which happens to be the first topic in The Will to Power.
That Loughner was reading Nietzsche on nihilism fits so perfectly into a template for such tragedies that it's easy to miss the gaping confusion in news stories about the shooting. These stories echo claims by some acquaintances that Loughner was a nihilist, and by others that he was "obsessed with nihilism," as if these are the same thing. But Loughner didn't see himself as a nihilist. He saw himself as fighting nihilism. This is evident in his fixation in his YouTube videos on the idea that words have no meaning, or have somehow lost their meaning in a process of nihilistic decline—a fixation that seems to lie at the basis of his tragic grudge against Gabrielle Giffords.
Nietzsche, oddly, has suffered a similar fate. Because of his assault on religion and rationalist metaphysics, and because of the hints of anarchy in his assorted visions of the future (e.g., "the transvaluation of all values"), he's taken as the West's über-nihilist. But he saw himself as the scourge of European nihilism, and possibly also its remedy. Nietzsche saw nihilism as a disease, which grows from, in Alexander Nehamas' words, "the assumption that if some single standard is not good for everyone and all time, then no standard is good for anyone at any time." It presents itself as mindless hedonism and flaccid spirit, but also as fanaticism.
So does that make Nietzsche and Jared Lee Loughner philosophical brethren after all, joined in the same fanatical fight against nihilism? In a word, no, and Loughner's pathological fixation on the meaning of words is the giveaway. One way of looking at Nietzsche's project is that he set out to teach himself and his readers to love the world in its imperfection and multiplicity, for itself. This is behind his assaults on religion, liberal idealism, and utilitarian systems of social organization. He saw these as different ways of effacing or annihilating the world as it is. It is behind his infamous doctrine of the Eternal Recurrence—in which he embraces the "most abysmal thought," that the given world, and not the idealizing stories we tell of it, is all there is, and he will affirm this reality even if it recurs eternally.
Jared Loughner's despair that everything is unreal and words have no meaning amounts to hatred of the world (a mania of moralism and narcissism) for its failure to resemble the words we apply to it. Faced with a choice between real people and some stupid abstraction about words, themselves mere abstractions, Loughner killed the people to defend the abstraction. This, then, really is a kind of nihilism, only not the kind that people think Nietzsche was guilty of. It's the kind of nihilism that Nietzsche was trying to warn us about, and help us overcome.
Thanks to Cris Campbell of the University of Colorado for some key insights and background on Nietzsche and nihilism.