Gory evidence no tabloids must get wrong (10)
I believe the answer is:
bloodstain
'gory evidence' is the definition.
'no tabloids must get wrong' is the wordplay.
'must get wrong' is an anagram indicator.
'no'+'tabloids'='notabloids'
'notabloids' is an anagram of 'BLOODSTAIN'.
(Other definitions for bloodstain that I've seen before include "Sign of an earlier wound" , "Discoloration" , "One is potential evidence" , "criminal evidence" .)