How was he certain he could initiate a kidnapping: sucessfully enter the house, not raise alarm from the occupants, not get a hassle from the dog, locate and carry out a child without a fuss, not be seen while out on the sidewalk, etc., etc.
Why would a Mensan killer then not clean out his computer of incriminating porn, not discard clothing with potential blood stains, not clean out his sink traps, make comments about "good places to leave bodies", etc?