Remorseless

Adjective

 * 1) without remorse, mercy or pity
 * 2) unyielding or relentless

Thesaurus
bowelless, callous, cruel, dog-eat-dog, flinty, griefless, hard, harsh, heartless, impenitent, implacable, inclement, inexorable, merciless, pitiless, regretless, relentless, ruthless, savage, shameless, sorrowless, unashamed, uncompassionate, uncompassioned, uncontrite, unfeeling, unforgiving, ungrieving, unmerciful, unpitiful, unpitying, unregretful, unregretting, unrelenting, unremitting, unremorseful, unrepentant, unrepining, unrueful, unsorrowful, unsorrowing, unsorry, unstoppable, unsympathetic, unsympathizing, unyielding, without mercy