86. 

This incident took place on the island of knights, liars, and normal people. Let's recall that knights always tell the truth, liars always lie, and normal people sometimes tell the truth and sometimes lie.

Three islanders, A, B, and C, appeared in court. It is known that the crime could have been committed by only one of them. It is also known that the one who committed the crime was a knight and that there were no other knights among the three defendants. At the trial, A, B, and C made the following statements:

A: I am not guilty.

B: This is true.

C: B is not a normal person.

Who among the three is guilty of the committed crime?
86. Defendant A cannot be a knight, for if he were a knight, he would be guilty and would not lie, claiming that he is not guilty. Defendant A cannot be a liar either, for if he were a liar, his statement would be false, and he would be guilty and, consequently, a knight. Therefore, A is a normal person and not guilty. Since A is not guilty, the statement of islander B is true. Therefore, B is not a liar: he is either a knight or a normal person. Suppose B were a normal person. Then the statement of islander C would be false, and C would be either a liar or a normal person. This would mean that among the three islanders A, B, C, there is not a single knight. Therefore, contrary to the conditions of the problem, none of them is guilty. From this, we conclude that B cannot be a normal person. He must be a knight and, therefore, guilty.