Before I arranged bail, this might serve as an excuse (5)
I believe the answer is:
alibi
'an excuse' is the definition.
(excuse given by a suspect in an investigation)
'before i arranged bail' is the wordplay.
'before' is a charade indicator (letters next to each other).
'arranged' indicates anagramming the letters (letters rearranged).
'bail' with letters rearranged gives 'alib'.
'i' put after 'alib' is 'ALIBI'.
'this might serve as' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for alibi that I've seen before include "Proof of not being at crime site" , "Legal defence - was elsewhere" , "Justification" , "that gets him off the hook?" , "Legal proof of innocence" .)