My opinion only:
I am in agreement with those who believe that the murderer was/is local. Likely someone living close by. Someone who knew their way around the back ways and knew that at that hour on those pathways that he/she would not likely encounter anyone in the short distance that would be traveled. Someone who has demonstrated anger, violated personal friends, relatives, etc. Perhaps a neighbor who had grown infuriated with the noise, partying at all hours, jealous of their fun, their youth. So, the “residence” issue comes into play. Perceived exclusion. No doubt LE has some individual in mind. Don’t rule out a female.
I am not convinced the person had previous homicidal experience. But, no doubt has demonstrated strong ego ~~~ like, “I’m smarter than everyone, I’ll never get caught” attitude. No stealth murderer ever believes that they will get caught. The criminal mind is largely impervious to self-doubt. Thus, likely some criminal background.
I have confidence in LE. It’s just a matter of time.