I'm sure that the suspect was well aware of how a young boy would react to being attacked. The suspect had done the same thing 9-10 months earlier. He would have been more practiced at ensuring that his victim could not escape when he abducted Jacob.
But there was one key difference: he had a gun this time. And the tracks the two of them left in Rassier's driveway suggest DH was supremely confident the gun would talk for him.