Behind Bobby Lau, Dillon is already imagining the proper spot on the man's back to hit his heart. It's a little trickier from the back... You have not only ribs to miss, but a spine and shoulder blade as well.
Unless he just punched straight through bone and sinew without any thought to finesse.
Kind of harsh, but at least it doesn't make the sort of mess a fresh corpse does. What with the bleeding and defecation and all.