The Collaborative International Dictionary of English v.0.48:

Unremorseful \Unremorseful\
   See remorseful.

WordNet (r) 3.0 (2006):

unremorseful
    adj 1: not penitent or remorseful [syn: impenitent,
           unrepentant, unremorseful] [ant: penitent,
           repentant]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "unremorseful":
   bowelless, cruel, dog-eat-dog, flinty, griefless, hard, harsh,
   heartless, impenitent, inclement, inexorable, merciless, pitiless,
   regretless, relentless, remorseless, ruthless, shameless,
   sorrowless, unashamed, uncompassionate, uncompassioned, uncontrite,
   unfeeling, unforgiving, ungrieving, unmerciful, unpitiful,
   unpitying, unregretful, unregretting, unrepentant, unrepining,
   unrueful, unsorrowful, unsorrowing, unsorry, unsympathetic,
   unsympathizing, unyielding, without mercy