Criminal sinned when stealing church's cross (8)
I believe the answer is:
incensed
'criminal sinned' is the definition.
I can't tell whether this defines the answer.
'stealing church's cross' is the wordplay.
'stealing' means one lot of letters goes inside another.
'church' becomes 'ce' (abbreviation for Church of England).
'cross' becomes 'innsed' (I can't explain this - if you can you should believe this answer much more).
'ce' placed into 'innsed' is 'INCENSED'.
'when' is the link.
(Other definitions for incensed that I've seen before include "Cross" , "in a lather" , "Infuriated, outraged" , "A high church may become so" , "Livid" .)