As those who have followed this case from the beginning know, there's unfortunately very little public information out there to work with. I have only recently acquainted myself with Scott's murder. One thing that I have gathered that has been touched on here before, is that IMO, the day Scott was murdered (a Friday) he took the day off work. I think this could considerably narrow the field of suspects because how many people would know this, or plan for this? I think we can presume that there's no concrete digital trail between Scott and his murderer, or at least not one pointing to communication between the two on the day he was killed. If there was, I think we would have seen more movement in the case. So, we have someone dressed with the intent to conceal themselves arriving at Scott's shared apartment on a day Scott has taken off work. This person was able to gain access to the apartment. What are the possible scenarios allowing this person to gain entrance?
1. Scott opened the door for someone he did not know
2. Scott opened the door for someone he did know
3. The murderer broke in with force (we have no indication of this but with a lack of information I don't think we can definitively rule it out)
4. They had a key
From our informative posters here who lived at the building, we have learned that there are no cameras beyond the first floor so movement in the hallways between residences is not monitored. This would allow the killer to remove any clothing without detection, including his balaclava/mask, so that Scott would see his face at the door. We don't know if the killer was aware of this fact or if they were simply lucky - assuming they did this.
Unfortunately without knowing Scott's disposition or his aversion to risk, we can't say with much confidence whether he would open the door for someone he didn't know or if he would open the door without looking through a peephole. All we've really been told is that Scott was apparently "caught off-guard" by this person. Whether that means caught off-guard inside the apartment after letting the person inside, or caught off-guard at the door, we can't say for sure.
Returning to my initial point - I think the circumstances surrounding Scott taking the day off work and the pool of people who would have been aware of this in time to plan this murder is a very, very important element to hopefully one day solving this. I imagine the police have attempted to compile a list of people who fall under this category. An optimist could even go as far as saying they have identified a solid suspect out of this group and they are trying to find more concrete evidence to satisfy an arrest.
The wild-card? The killer went to the apartment for a different reason and was not anticipating Scott would be home, at which point they improvised and it resulted in Scott's death. Personally, I don't view this scenario as very likely but I also don't think it is without merit.