Responses
Its kinda up to interpretation but to what i got from it was that he enjoyed killing them, and the true guilt he felt all along was that enjoyment he got out of killing 10 people. Thats why whenever he was happy he felt bad about it because he could never forget the happiness he felt in that moment and knew it was wrong (idk tho thats just what i got from it :P )

Can someone help explain the very last panel? Is it the idea that he was happy with it? That me meant to do that? And the rest of the story is him living with the guilt of his happiness? That’s some things I see online but I’m still somewhat confused