Solution to: Thoughtless Thief

The fact that lies have been told and that all six suspects have been called "innocent" at least once means that the guilty party is among the arrested suspects. Furthermore, if one of the suspects lies about the innocence of person X, this also applies to all others who claim that person X is innocent.

Suspect B has been labeled innocent twice, suspects A, D, E, and F have each been labeled innocent three times, and suspect C has been labeled innocent four times.

Since four lies have been told, the culprit must be the suspect who has been mentioned four times, which is therefore suspect C.

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