Senseless victims in the crime bled horribly (5,5,4)
I believe the answer is:
three blind mice
'senseless victims' is the definition.
(they lacked the sense of sight)
'in the crime bled horribly' is the wordplay.
'horribly' is an anagram indicator (a horribly wrong version of the letters).
'in'+'the'+'crime'+'bled'='inthecrimebled'
'inthecrimebled' with letters rearranged gives 'THREE BLIND MICE'.
(Other definitions for three blind mice that I've seen before include "tailed by the Dutch?" , "Characters in rhyme" , "Nursery rhyme" , "Nursery Ac" .)