Warrant ends in your alibi arrested by police (5)
I believe the answer is:
merit
'warrant' is the definition.
(I've seen this before)
'ends in your alibi arrested by police' is the wordplay.
'ends in' indicates one should take the final letters.
'arrested by' means one lot of letters goes inside another (inserted letters are held or arrested).
'police' becomes 'met' (London Metropolitan Police).
The last letters of 'your alibi' are 'ri'.
'ri' going within 'met' is 'MERIT'.
(Other definitions for merit that I've seen before include "credit" , "Goodness" , "distinction" , "Excellence, desert" , "Worth; deserve" .)