The topic comes up often on firearms boards & forums.
I have wrote about how the NYPD surgeon suggested aiming for the lower torso to the late Jim Cirello(check correct spelling), a highly respected NYPD officer & FLETC instructor;
www.fletc.gov .
It makes a lot of sense to aim for the lower torso but with handgun calibers, there is NO absolute way that 1 or 2 rounds will ALWAYS drop a violent felon or be able to end the critical incident. Handgun calibers, even the .45acp or big .44magnum are not going to end shoot-outs with 1 round 100% of the time. The large size may help but there is no way of knowing exactly how or where a fired round will act in a bad guy/gal's body.