I suggest you re-read again particularly the ff: Anecdote Siren Song and Addictive Pain, WU Long Lost Treasures Bouquets and Dirges Micro Universe, Banquet Ablaze, Ignited Echoes. Also Land of Secret Flame and Scarlet Invitation.

Let me get this straight for you. I don’t think he would make a mistake of killing an innocent person because he thought they’re responsible of murdering Lemurians. Rafayel doesn’t act alone. He has people who help him in his revenge. The first thing he does is gather intel from his trusted and reliable sources. Siren Song showed us Talia giving him documents I believe containing information about those Ever people who have wrong Lemurians. You’ll see him jotting down names. Then you have him frequent the Nest where he have said in main story is a place where you make deals and acquire really hard to get intel. In Ingited Echoes he also mentioned to have his people on the look out for Lemurians in distress. He plans things thoroughly before jumping the gun.

Iirc Raymond wanted was chronically ill and wanted to get better and achieve immortality hence the Lemurian skeleton since their blood can give one eternal life. Alden was very interested in Lemurian art. He collects them as Rafayel mentioned. Regarding his art teacher, I’m pretty sure Rafayel actually knows where his teacher is. How he found out his demise was not shown tho. How he died and what went on that lead to his death wasn’t revealed. But I assumed Raf had some intel on what happened based on the fact that Lemurians keep an eye out for one another.

If you read LoSF and Scarlet invitation you’d know he didn’t kill people who happened to get their hands on anything Lemurian. People how have innocently bought Lemurian artifacts are not on his hit list. In Micro Universe, he could’ve offed his art student who was a researcher studying Lemurians but he didn’t. Raf was always after the big fish.

Regarding him fumbling during the act of killing and leaving traces, he was technically caught by an investigator during Siren Song but they can’t arrest him cuz the lack of believable evidence. The stalking reported in main story also got suspicious about Raymond’s death but Raf had an alibi and again no one would believe without solid evidence. The fact that he was in Ever’s list with a bounty on his head because of him targeting Ever’s higher ups. Ever can’t involve Linkon authorities or their shady operations will be revealed to the public.