What makes this case the most frustrating case I've ever followed is that we know almost nothing yet it seems like the police are completely dependent on a tip coming forward. But how are tips going to come forward when all they've offered up to the public is an inaccurate sketch for two years and a short audio recording? Seems like they're waiting on a miracle. Hope I'm wrong obviously.
I think like most crimes involving strangers it was a crime of opportunity. Guy saw two teenagers walking alone. He passed them, maybe even had a brief conversation with them, walked passed them to see if anyone else was coming, then doubled back, the girls knew something was up, they took his picture and started recording. The presence of a "kill kit" would be an indication of whether this was planned or not but I bet he carries a utility knife/hunting knife with him at all times.
My first inclination is that the murderer works some manual labor job, probably a contractor of some sort. Not just because of what he's wearing but because he's going for a walk on a Monday afternoon in February. February is one of the least popular months for employees to take vacation time. So it's likely that he just doesn't work a job that has a set schedule or just has Mondays off usually because he has to work Saturdays. Trivial information I know considering the amount of people that work manual labor and have Mondays off. If we knew what the murder weapon was we could make a better educated guess of what he does for a living.
But the most important part of his appearance is absolutely that flat cap. IF it's accurate that he was wearing a flat cap and IF he had red hair he's probably rocking the flat cap because he wants people to know of his irish heritage. I wouldn't be surprised if he participated in something Irish related, even if it's just some small social thing, or maybe he has some role in the Catholic church. Unfortunately too much time has passed. No way this guy is wearing a flat cap anymore.