I think everyone here is getting too caught up in the gait and what it means. Yes, the gait is distinctive, but sometimes people walk in different ways at different times, depending on their mood, posture, whether they're carrying something heavy, etc. Differences in the gait do not equate to this being pictures of two different people. Also, it would not make sense for this to be a woman. The APD already said Male, and they've been considering this for a year. Also, given the already present height difference between Scott and the attacker, it would be very difficult for a woman to overtake him.
My condolences to those affected by this tragic murder, and I hope the person who did this is swiftly brought to justice. My first instinct was a drug-motivated killing but assuming Scott's family and friends are being truthful about him not being involved in the drug scene, that should be ruled out. If Scott was involved with drugs it would certainly be known to his friends. If there was concern about post-death reputational harm, and family and friends suspected drugs, there would not be this push to find the killer (and the killer would probably already be known).
Here are my thoughts now:
The outfit, use of bleach, and overall "clean" killing all indicate a professional hit, or at least a hit by someone with some experience in this area. Others speculated about Scott being involved with foreign intelligence actors but I think its a bit more local, such as connections with a local gang.
I believe the key to this case may be in Scott's girlfriend at the time of this death. I do not mean to speculate that she was in any way a willful participant or conspirator in the murder, but I believe the motive may have had something to do with her. I have sincere and heavy sympathy for her loss.
Scott's friend in this message board mentioned the couple had been on and off for ten years and were currently on. Breaks in the relationship indicate there may have been a jealous male spurned by the girlfriend when her and Scott got back together. (Another possibility, although not aligned with my overall theory, is that Scott spurned a woman when he got back together with his long-term girlfriend, and that woman asked a male friend, brother, or professional hit man to get revenge on Scott.)
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Again, my condolences to everyone involved in this case.