I really hope it is a solid lead.
Would a young man the POI's age: if still a stranger to locals, and to fans of the bands attending BM's bash, to the bands themselves, to the whole scene and to all the people attending previous PAP and other concerts, a complete unknown still, more than a month after, then somewhere maybe farther away, it may be possible some person who sees this young man more often than others, may have noticed something about him that was odd. He may have a rung a bell with the sketch and being away the day of the concert and perhaps thereafter, oddly, abruptly, out of pattern, with somebody around him. He would have a car, cameras maybe, black hoodies, wigs, masks, hats, he may or may not wear glasses, be awkwardly talkative with young blond women, not in a group, or part of one who returns on his own? He exists, and somebody has noticed something about him that sparked some doubt, fear, discomfort or just similarity. It's hard to get yourself to say something, but being wrong doesn't make you any less brave for speaking up, when it crosses your mind, it seems to me, from all I've read, seen or heard in the various cases from the people who did say something.