@Mick96
The size of the town isn't firmly established, but I'm going to say after the devil has made himself extremely visible on four different very public executions that the majority if not all the guards know what he looks like now, and, more importantly, know what he dresses like given that he wears the same jacket and producing black clothing is almost as difficult as making purple clothing back in the medieval age. He's the only one in a general crowd that has an incredibly expensive black jacket and it's the only one he wears. The town doesn't look big enough to support having a massive amount of guards that he someone hasn't been seen by all of them. Furthermore, it was already established in the first chapter that the guards were familiar enough to identify the first witch on siight, even without a written description, so there must be some system in place for describing the individuals they are looking for.
Furthermore, they happened to apparently be on an incredibly public street, so I don't know why no one in the audience pointed out that 3 individuals had just been consorting with the witch that had been arrested, since you would think from all the torturing going on for information of other witches that the public would not also be concerned with those who had just been immediately buddy buddy with said arrested witch.