Criminal act, one perpetrated in prison? (6,3)
I believe the answer is:
inside job
'criminal act' is the definition.
(a crime committed with assistance from inside)
I cannot understand how the remainder of the clue works.
(Other definitions for inside job that I've seen before include "Crime by someone with special knowledge of the target" , "that an office worker experiences?" , "Crime of one hired before" , "breach of trust" , "Case" .)