The Collaborative International Dictionary of English v.0.48:

Exculpate \Ex*cul"pate\, v. t. [imp. & p. p. Exculpated, p.
   pr. & vb. n.. Exculpating (?).] [L. ex out + culpatus, p.
   p. of culpare to find fault with, to blame, culpa fault. See
   Culpable.]
   To clear from alleged fault or guilt; to prove to be
   guiltless; to relieve of blame; to acquit.
   [1913 Webster]

         He exculpated himself from being the author of the
         heroic epistle.                          --Mason.
   [1913 Webster]

         I exculpate him further for his writing against me.
                                                  --Milman.

   Syn: To exonerate; absolve; clear; acquit; excuse; vindicate;
        justify.
        [1913 Webster]

WordNet (r) 3.0 (2006):

exculpate
    v 1: pronounce not guilty of criminal charges; "The suspect was
         cleared of the murder charges" [syn: acquit, assoil,
         clear, discharge, exonerate, exculpate] [ant:
         convict]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "exculpate":
   absolve, account for, acquit, amnesty, clear, condone,
   cry sour grapes, decontaminate, destigmatize, discharge, dismiss,
   dispense from, do justice to, excuse, exempt, exempt from,
   exonerate, explain, forgive, free, give absolution,
   grant amnesty to, grant forgiveness, grant immunity,
   grant remission, justify, let go, let off, nonpros, pardon, purge,
   quash the charge, rationalize, rehabilitate, reinstate, release,
   remit, restore, set free, shrive, spare, vindicate, warrant,
   whitewash, withdraw the charge