How can a Muslim denounce evil if its perpetrator is not identified from among two people?

If a reprehensible act has been committed and concluded, do not seek out the perpetrator, and it is impermissible to spy to uncover them. Disobedience is of three types: that which has occurred and concluded, the punishment for which rests with those in authority; that which is currently happening, which must be denounced according to one's ability; and that which is anticipated, for which only admonition and preaching are required. It is not legislated for you to search or inquire about the one who committed the reprehensible act, but if you deliver a general admonition explaining the prohibition of the act and the necessity of repentance from it, that would be good.