Hilchos Lashon Hara chapter 6, section 11

Even when one is permitted to suspect the person spoken of this is only to guard oneself from harm. G-d forbid to do any action or cause him any harm or evil. Even if a kosher witness testified against him in a beis din, this only helps if he swore to the story’s veracity. Even more, even to hate him in one’s heart is forbidden by the Torah and one certainly cannot free oneself from any obligations one has towards him.