Lott isn't the only individual who has done done these types of studies.
Gary Kleck of the University of Florida has done similar studies, and reached conclusions similar to Lott.
In fact, Kleck started out trying to prove that guncontrol would lower crime rates, but was intellectually honest enough to admit that when he compiled the evidence and crunched the numbers, the reality didn't support his initial hypothesis.
In the mid eighteenth century, Cesare Beccaria, a european criminologist also concluded that laws that prohibited the carrying of arms only improved the criminals' chances of completing their crimes.
Thomas Jefferson, IIRC, quoted him on atleast one occasion.
I have heard that there have been attempts to discredit John Lott; the referenced sight here seems to be a
Wikipedia source which causes me to atleast suspect it's bona fides. In anycase, he was part of a study conducted by the University of Chicago along with a Dr. Mustard ... has he been similarly discredited, I wonder?
This is the sort of thing that happens when you try to do statistical studies and crunch numbers to defend a God-given Constitutionally provided for right.