Laws of Lashon Hara / 7: 10-12 (61)

10. One who hears lashon hara and there are recognizable signs that prove that the information is in fact true, if the information is not only about a negative personality trait but a truly wicked act, if it is impossible to judge him favorably, one can believe it.

11. This authorization is only when the recognizable signs are definite and obvious, not superficial. Also the listener must have seen firsthand these recognizable signs.

12. Even when the listener is allowed to believe the lashon hara, he is forbidden to pass it on, and he is forbidden to cause the subject monetary or physical harm based on what he has heard.