Even if the blood slides are found....they'd have to find his dump site/body parts like in S2. And yes, there may be some fibers or other forensic evidence they could link to him.....as to how well he cleans his kill tools? That I don't know, but you'd think he'd have learned something from his close call in almost getting caught as the BHB.
Maybe someone will
suspect him and follow him and catch him in his kill room with Trinity on the table. He'll then have a choice: allow himself to be caught or kill someone innocent to stay free and with his family and continue his 'work.' That would certainly be shocking.
We know he gets Trinity because we see him getting the needle to the neck. Just don't know if Dex will kill him.
Someone else pointed out that the teaser says something like ".....change both their lives forever..." (Dex and Arthur) which kind of makes it sound like they'll both live....
We could speculate on this til Sunday and probably still not guess correctly!!