First off how do you know the second shot disabled? Maybe you have ice water in your veins and perfect shot placement and x-ray vision to know exactly where the second shot went, but this isn’t TV and you aren’t Jack Bauer/James Bond/Dirty Harry
It might have also missed, or been just a nick in his arm. Self defense training and Police training all train that you keep pulling the trigger until
A) the suspect is down
or
B) The gun goes click in which case you reload.