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An individual was killed. There are 4 suspects.

A says C is the killer.
B says C is the killer.
C says that B is mendacity.
D says that it wasn’t him.

There is just one individual telling the reality. Who is that this individual, and why?

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This reply’s just a little eccentric, however bear with me. (Warning: this reply would match a puzzle, however since it’s not explicitly a puzzle, simply deal with this as light-hearted leisure.)

There is not any killer.

Suppose the narrator is telling the reality that there’s just one individual telling the reality.
Then the narrator is the reality teller, and all of the others should be liars. But since B is among the many liars, C’s assertion is true, which contradicts the supposition (we now have 2 fact tellers: the narrator and C).
So the narrator is a liar, and the preliminary assertion “An individual was killed” is fake. Since no one was killed, there isn’t any killer. 😛

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