Mafia 31. Twilight Dances.

Morni, the Thief only deprives someone of their vote; he doesn't use it himself. Look at the situation yourself. Right now, the situation is 10/6/1. We execute the Archer. It becomes 10/5/1. We will probably lose two of our own (I am deliberately considering the worst-case scenario). 8/5/1. We execute the Mafia member we know, if we don't find other Mafia members with a high probability. 8/5. A kill – 7/5. Now, remember the vote deprivation – if we allow another kill in the 7/5 situation without executing a Mafia member (and this is likely, as it's not always easy to convince the majority of townspeople with just one piece of evidence), we will lose. Another option: we execute the Avenger now. We are left with 10/6, with the Archer identified. At night, we lose one, and during the day, we execute the Archer – 9/5. I don't think the Mafia will naively risk sending the Archer on another mission again – the Knight acts before her kills, and we can block her. So, there will be a new killer and new evidence, probably. In this situation, the risk is lower, in my opinion. As you can see, in the same two days, the situation will be 8/5 or 9/5 – it's obvious that the latter is better. In addition, as Slonik said, at a certain point, it will become problematic to execute a Mafia member – we shouldn't delay this.