There was a phenomena that can be linked between them. Remember how Matsuda (that idiot) thought that maybe Kira was right in laying judgment down on criminals? During the 2nd season when Dexter's old kills were discovered and they were trying to figure out who killed them, a lot of people referred to him as the "Bay Harbor Butcher". Some people called him justice because after some investigation, it turned out that the bodies were all in prison at one point for murder, or at least tried for it.