Chapter 970 gave some hard evidence on the traitor. Ashura Doji was stabbed in the back.
The panel implies that it’s the hand of King, but we know that King have dark hands.
Every time King appeared he had completely black hands. Also every Scabbard has very distinctive arms or hands, sometimes with gloves (like Inuarashi) or special skin (like Kawamatsu). The hand that is stabbing Ashura Doji has a ring bracelet and the only character that has such a bracelet is Denjiro.
The panel with King after the stabbing is a distraction. Also there is no way Ashura Doji will give his back to the enemy he is facing. So I think he was facing King, but was stabbed in the back.
*by axyaxy