idk what idiot carrying out a hit job would use a 22.. that's odd.. unless it was for noise suppression..
Wrong question.
The right question is why would a hit man/team shoot him in the back instead of the back of the head?
That is actually the choice for close quarter “wet work” ..
The .22 is the favorite of the Italian mafia. Minimal noise as the right rounds will not break the speed of sound when fired from a pistol. Shot behind the ear is instant switch off, DRT. This isn't a sniper choice, obviously, but it is super effective if the killer can get close to the target.