Laws of Rechilus / 6: 10 (107)

10. One whose business has been harmed as a result of slander, and there are ‘recognizable signs’ that so-and-so is the culprit, it is forbidden to inform on him. It is only permitted in the following case: A. It will prevent the culprit from further slandering him. B. There is no other way to prevent him from slandering him. C. He saw him slandering him with his own eyes, as it is not enough to rely on ‘recognizable signs’, and all the more so not to rely on others.