Rambo's selective mercy?

Question

In First blood 1 and 2, Rambo plows through all but doesn't kill the boss at the end.  In Last blood he killed everyone but the terrible dad and traitor friend.  Why?

Answer 1

did you watch the movies?

Answer 2

He didn't kill anyone in first blood. He maimed a bunch, and the one guy that fell out of the helicopter was kind of his own fault.