The Collaborative International Dictionary of English v.0.48:

Inculpableness \In*cul"pa*ble*ness\, n.
   Blamelessness; faultlessness.
   [1913 Webster]

WordNet (r) 3.0 (2006):

inculpableness
    n 1: a state of innocence [syn: blamelessness,
         inculpability, inculpableness, guiltlessness]