Hilchos Lashon Hara chapter 6, section 11

Many people make mistakes about this when they hear lashon hara in a case where it is allowed to "be cautious." The general rule is that one may be cautious about lashon hara only to protect oneself from that person. But Heaven forbid to do anything against him, or to cause him any harm.

Even if the lashon hara came from one kosher witness who testified against him in a beis din (Jewish court), it only matters for an oath, but it does not allow harming him. More than that: it is even forbidden to hate him. And one is not freed from the duties the Torah gives toward him (like tzedakah and similar things).