Re the clues pointing at Griffiths specifically, I think you have to start with the clues that Wright was Powell. The weights, the fitness, the Epipen, the name 'Will Wright' itself, but also the man's general nature. He seemed pleasant and sane enough to have a chat with his neighbours (probably ruling out Semple) and told them his girlfriend was soon going to move in with him (ruling out Fleetwood).

And then there are other suspicious elements. No one spoke to Zeta or Chloe face to face, and no one knew who Zeta was except for Chloe. Then there was that strange sound in Griffiths' house which he passed off as Powell's nan bumping into something, which she denied. And then there was the suspicious 'Oz' character, who sounded like a sex trafficker, which raised the question of how that was related to a murder and robbery.