The Collaborative International Dictionary of English v.0.48:

Culprit \Cul"prit\ (k[u^]l"pr?t), n. [Prob. corrupted for
   culpate, fr. Law Latin culpatus the accused, p. p. of L.
   culpare to blame. See Culpable.]
   1. One accused of, or arraigned for, a crime, as before a
      judge.
      [1913 Webster]

            An author is in the condition of a culprit; the
            public are his judges.                --Prior.
      [1913 Webster]

   2. One quilty of a fault; a criminal.
      [1913 Webster]

WordNet (r) 3.0 (2006):

culprit
    n 1: someone who perpetrates wrongdoing [syn: perpetrator,
         culprit]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

CULPRIT, crim. law. When a prisoner is arraigned, and he pleads not guilty,
in the English practice, the clerk, who arraigns him on behalf of the crown,
replies that the prisoner is guilty, and that he is ready to prove the
accusation; this is done by two monosyllables, cul prit. Vide
Abbreviations; 4 Bl. Com. 339; 1 Chit. Cr. Law, 416.