A recruit would be the person who becomes enrolled or becomes a member. A new soldier would be a recruit. A recruiter would be the person who brought the recruit into the organization. The army has recruiters to find new soldiers. This is true of most words that have -er added to the end. The action is performed "by" the person with -er, not "on" them. So the killer is the bad guy (the one that killed someone else), not the dead man (who was killed).