What is it worth to help him in exchange for information about the cult. I agree that you shouldn't trust him (he should also be taken into custody, but oh well). But there is no need to immediately condemn him. We don’t know what prompted him to join the cult and what he did there.Aha, what is the point of all this?
It doesn't matter if you follow the baron's line or not. In the first case, you need to at least try to arrest all the perpetrators and conduct an investigation. In the second case, you are just some kind of murder hobo. If everyone is to be executed indiscriminately, then at least one must have the right to do so. What will be available, as mentioned in this thread and others.