[ThunderSleeps]

...the customer pulled out a concealed weapon and shot the suspect in the chest once. The gunman was pronounced dead at the scene.

That was some mighty fine shooting. One shot, no question, DRT.

My SOP when carrying my 9mm is (barring special circumstances) if I shoot, I shoot #1 center mass and immediately follow up with #2 to the head. Then I'll evaluate the target. I figure the center mass is the high percentage shot, while the head shot has the biggest chance of stopping the perp in their tracks. If I'm carrying my .45 (a full size S&W stainless 1911) I'll go with just the center-mass shot then evaluate.

[MHGinTN]

Center mass first, because it tends to freeze the target long enough to make an aimed shot to the head. It works even with a .22lr, so carry and practice, whatever you choose to carry. (The Ruger SR22 is a very nice .22lr for carry; magazine followers changed out can give 14 rounds in the magazine and one in the chamber for double action first round.)