This was carefully planned IMO. I suspect that the entry and exit route was walked ahead of time by someone, even if it was not the assassin. I have for instance on rare occasions seen people walking on my property, and when I went outside on my porch to ask them what they were doing, they said they were looking for a lost cat or dog. Once I could see the dog running along a fence, and the other time, I knew the guy in the neighbourhood who lost the cat. I also asked two men, wearing bright orange vests what they were doing walking down my driveway, and they said they were from the public works, looking over my fence because they needed to know something about my neighbour's property, and he was not home. I think all of these were valid, but my point is that someone caught trespassing could come up with some plausible excuses.
My guess is that the entry route to the Sherman home would have been more risky than the exit route because there would have been more people outside walking, coming home from work, shopping etc. or just looking out a window. It is really interesting that the police say that this guy can be seen coming very close to the Sherman property, staying there during the time frame of the murders, and then leaving. If they collected video evidence in a 3 Km. radius around the house, one has to wonder where they first, or last saw him. That could provide crucial evidence if they saw him with someone else, entering or exiting a vehicle, etc. He may have also changed his appearance somehow when walking in, from the way he looked walking out, that is, different type of cap, scarf, or as someone here has wisely suggested, using a reversible coat. Perhaps that is why police drew special attention to the gait and height. I also remember that in the weeks after the murders, I read somewhere, I think in a newspaper article that police were interested in two people, a man and a woman, walking a dog in the area. That might have been a good cover on the way in, if he walked part or all of the way with someone else and a dog. Just some thoughts. IMO