Thank you for the very detailed and insightful feedback! The video helps a lot going through how a new player might approach the game.
You are quite right to point out the ambiguity of the wordings and the card designs. During development, I just thought it doesn't make a lot of sense for a suspect to call other suspects "suspects" so I ended up with "witnesses". For now, both the the terms just mean "person" without indication of guilt or innocence. The adjacency rule indeed includes diagonals as in minesweeper but I shouldn't really make the assumption that the player knows about that. A glossary in the tutorial explaining the different terms would probably go a long way.
p.s. The chef on your first run said "closest to the Count" but you counted "distance to chef". He was innocent because the Butler is next to the Count thus being closest.