Secret Conflict Resolution in GMless systems? Suggestions Wanted!

I am in the process of designing a role playing game based on the works of Edgar Allen Poe, and have run into a problem. I want to have it be GMless to emphasize the isolation present in a lot of the fiction, but I am struggling to find a way for there to be secret attacks between characters without a referee of some sort.

The basic chassis is like games such as Werewolfs, Town of Salem, or Mafia where the players each have a secret role/job that gives them their goal in the game. Often this involves killing another player. I want a way for these attacks to be anonymous, but with a die roll + modifier resolution system. My current idea is that each player has a deck of cards. During the night time part of the round (one player has their head up at a time), if they are performing an anonymous action they roll a d10 (d8?) and add their appropriate modifier. Then they take the card of the appropriate value corresponding with the total and suit corresponding with the type of action, and put it in front of the player who is the target, maybe in an envelope of some sort. On the day time part of the round (all players can freely interact), the players open their envelopes and see which type of anonymous actions were taken against them. They compare the "attack" numbers to their "defense" constant and narrate the result of the action. Then at the beginning of the next night time phase each player in turn retrieves their cards.

This works, despite being kind of unwieldy, but I am struggling to find an alternative. I don't have a ton of experience with GMless games, so any and all suggestions are welcome.

I think you have it right with the Card system. You don't need to do it at night, you just need to have everyone give everyone a card, and force them to shuffle before looking at them. This means that some cards would be neutral, while some cards can also be good or defensive.

You could also have all Players always facing away from each other. If they are sitting in a circle, they don't necessarily need to be looking directly at one another. Characters can roll their dice, and pass those dice to other players without turning around. (A game where you don't actually look at the other players could be interesting, especially if you're going for isolation) You would, of course, need to navigate by sound, and others would hear the shuffling of your clothing unless there is something loud going on. (Like talking)

I've never been a fan of modifiers, which is why i'd suggest you don't include them. Consider including extra abilities and utility powers rather than stat modifiers. It keeps it simpler, and would help with the anonymity.

You could have a "Pass the Buck" system, where players all pass two cards from left to right, which have a player signifier (Such as a color or a number indicating a certain player) and an action underneith. If a player draws their own signifier they keep the cards, otherwise they pass it to the right. If all players pass them at the same time, then the intended target of the note will not know who it came from. (You can add two signifiers to be more tricky, with the first signified player removing the first signifier card to reveal a second signifier, forcing them to continue passing the card around)


So that's three. Hope it helps!