After a 1994 terrorist attack on a Jewish center in Buenos Aires, police were deployed to 35 Jewish institutions around the city; this 2004 AER paper by Di Tella and Schargrosdsky shows that car thefts on blocks where those police officers were deployed dropped almost 75 percent as a result.
As is the case with many papers in this genre, I found the identification strategy here to be convincing but wondered whether the finding is important. The authors motivate the paper by saying that Becker wrote about crime, and a lot of economists followed suit; that Becker’s theory predicts that police presence decreases the incidence of crime; and that empirical evidence is weak because the one paper that seemed not to suffer from endogeneity problems (Levitt’s famous paper exploiting political cycles in police spending) was shown to be inconclusive. Isn’t it a little disingenuous to say that the deterrent effect of police presence is a prediction of Becker’s theory? I suppose it technically is, but it’s also a prediction of the most basic common sense — so much so that if you found the opposite people would think you had done the experiment incorrectly.
It’s a well-executed paper but I suspect it doesn’t change anyone’s mind. It is so hard to find nice natural experiments where something interesting varies, especially if you’re not completely agnostic about what that “something” can be, e.g. if you have a substantive field of specialization.