This is an interesting case that I have just taken a bit of a deep dive into.
This is a situation where a low risk individual, who no one appears to have anything to gain or any other motive, is murdered. Something that is obvious is that this was a well planned murder targeting Scott directly. Anyone going to that much effort to mitigate risk is not going to knock on random doors in order to murder whatever unlucky victim happens to answer the door. Too many things left to chance; multiple people home, people not answering unexpected knocks, security cameras actually working etc. There are plenty of safer ways to just kill anybody. It was Scott he was after.
The murder happened at a time Scott would be expected to be at work yet the guy knew he would be there and would be let in. How else would the killer know he was off work? He could have called him at his office but that would not tell him if he was home alone. I’m less certain, but still strongly suspect, that Scott was expecting this visitor and buzzed him in. Scott knew him and trusted him enough to let him enter his apartment.
The motive would be the best clue but people are murdered for the flimsiest of reasons: jealousy, revenge, vindictiveness etc. It is also possible that someone become enthralled with the idea of committing a “perfect murder” and choice of victim was a secondary consideration. Still, Scott was bigger and taller than the perpetrator. He was hardly an easy kill. He was chosen for a reason. I’m wondering if it was someone from his past that his current friends were unaware he was still in contact with.