Researchers. There have been innumerable studies on the subject - but really it's common sense. If you're a criminal you're unlikely to be particularly adept at the art of deliberation - otherwise you would choose a different way of life. But for evidence here's a somewhat recent review: http://www.jstor.org/discover/10.2307/1147698?uid=3739920&ui...
In islamic countries with sharia law, nobody steals, since you risk loosing a hand. Not that I recommend that approach, but I'd be careful with such statements.
If that was the case they would not be whipping, beheading, stoning, maiming and executing people in these countries. (spoiler:they are doing all of these things).
It's like saying because of the death penalty there are no murders in states that enforce the death penalty. When in actual fact it looks like it poses no deterrent at all.