Four friends have been identified as suspects for an unauthorized access into a computer system, of whom exactly one has committed the crime. They have made statements to the investigating authorities.
Alice said, “Carlos did it.”
John said, “I did not do it.”
Carlos said, “Diana did it.”
Diana said, “Carlos lied when he said that I did it.”
If the authorities also know that exactly one of the four suspects is telling the truth, then who did it?