MathNet 2000 — Math Olympiad Vault Question 115

The clerk recording the statements of three defendants at a trial was rather careless. The record reads:
Carlo: The guilty person is ...ario.
Dario: The guilty person is Dario.
Mario: The guilty person is ....ario.
Knowing that the guilty person lied and at least one innocent person told the truth, what can be concluded?
(A) The guilty person is Dario
(B) The guilty person cannot be determined
(C) Carlo accused Dario
(D) Mario accused Dario
(E) Mario accused Mario.