Here is one of the saddest facts about language and culture that I have noticed in quite a while: the search pattern "before turning * gun on himself" gets tens or even hundreds of thousands of hits on Google.
Most grammatical six-word sequences are very rare. That is one of the things that made Kaavya Viswanathan's plagiarism so easy to spot. For a six-word phrase to be moderately common it has to be a fixed phrase of some kind, such as a cliché, an idiom, or a proverb. I made up the six-word phrase "before anyone had even noticed it" literally at random, and Googled it, and got only a single hit in all of the web's trillion words. But shooting rampages by suicidal maniacs have become so common (there was another one in Alabama yesterday) that "before turning the gun on himself" and "before turning his gun on himself" have become commonly encountered clichés in news sources.
The reason I don't give actual numbers is that it is hard to establish accurately
how many times a phrase occurs, using Google. (A commenter who signs himself Forrest below explains why.)
Through a weird and horrible coincidence, while I was writing this post (which I have entirely rewritten because it was so badly misunderstood in its first draft), unknown to me, a new shooting rampage was occurring in Winnenden, near Stuttgart, in Germany. The gunman must have been committing suicide just about the time I first posted. And sure enough, in the Daily Telegraph account of it the phrase "before turning the gun on himself" turns up once again (in a reference to an earlier incident in 2002). The BBC News website uses the phrase yet again, referring to a 2006 incident in Germany. The ITV News site uses the phrase of the Winnenden massacre.
Most of the comments that piled up below the original draft of this post simply cited phrases, or lists of phrases, that get huge numbers of hits. This was disappointing, not only because the result is boring, and didn't quite connect with my point, but also because it diluted the pool, so the three or four really interesting comments were hard to find. I have done a ruthless cull, and deleted all the ones that merely cited a phrase and said how many hits it got. (I probably should have deleted more. See the Language Log Comments Policy. It is not incumbent upon us to host in our comments area any random observation that floats across your mind.)
It is not surprising that phrases with high hit counts can be found if you go for formulaic ways of saying things that are often said (like "Email this page to a friend"). There are so many six-word phrases in English that there is room for thousands of them to have become clichés or otherwise familiar expressions. One commenter cited "of the United States of America", for example (this is really two or three lexical items rather than six: it has the same syntax as "of the USA", or "of France") — an even more deeply boring example than the many others. But even if there are thousands of high-hit-count six-word phrases, it can still be the case (and almost certainly is) that most six-word phrases are very rare.
Anyway, my main observation here is not about the rarity of arbitrary phrases. It is about the sad fact of this one having been called upon so often, as school massacres go on and on racking up their victim tallies.