Criminal one caught by the force (5)
I believe the answer is:
thief
'criminal' is the definition.
(thief is a kind of criminal)
'one caught by the force' is the wordplay.
'one' becomes 'i' (Roman numeral).
'caught by' means one lot of letters goes inside another.
'force' becomes 'f' (symbol used in Physics e.g. f=ma).
'i' put within 'the' is 'thie'.
'thie'+'f'='THIEF'
(Other definitions for thief that I've seen before include "Person who steals things" , "A robber or pickpocket" , "One who is fourth in line after a rich man" , "Larcenist" , "'Taffy was a - - '" .)