exculpation
    n 1: a defense of some offensive behavior or some failure to
         keep a promise etc.; "he kept finding excuses to stay";
         "every day he had a new alibi for not getting a job"; "his
         transparent self-justification was unacceptable" [syn:
         excuse, alibi, exculpation, self-justification]
    2: the act of freeing from guilt or blame

Exculpation \Ex`cul*pa"tion\, n. [Cf. LL. exculpatio.]
   The act of exculpating from alleged fault or crime; that
   which exculpates; excuse.
   [1913 Webster]

         These robbers, however, were men who might have made
         out a strong case in exculpation of themselves.
                                                  --Southey.
   [1913 Webster]