Cross tactics of the three sides
Exposing a rival
An Irish player can honestly point at an Italian one; an Italian at an Irish one. For the city such an exposure is useful, but it does not confirm that the accuser is a civilian.
Matching votes
A temporary match of interests does not mean a shared team. You need repeated, independent signs.
The double shot
If both gangs chose the same player, that player dies in any case. From a single death you cannot tell whether the targets matched.
The hidden queue
While both gangs are alive, the shot that counts alternates, and the host chooses the start. After one gang is destroyed, the remaining one shoots every night.