Excuse from Svengali Bill (5)
I believe the answer is:
alibi
'excuse' is the definition.
(excuse given by a suspect in an investigation)
'from svengali bill' is the wordplay.
'from' says the answer is hidden in the clue.
'ALIBI' is hidden in the letters of 'svengali bill'.
(Other definitions for alibi that I've seen before include "Claim put to court" , "Fact of being elsewhere (legal)" , "Legal defence proving innocence" , "that gets him off the hook?" , "Proof of not being at crime site" .)