Мафия 23. The Rockland tavern

On the first night, the Thief doesn't know any of the Killers and cannot plant evidence.

I don't understand the mechanics of this ability either. Maybe the Thief sends a message to the GM - "I'm watching N," and if that person is a Killer, the GM sends him a message - "N is a Killer," in response to which the Thief must send evidence? :confused: