Thoughtless prisoner lies about pinching book (13)
I believe the answer is:
irresponsible
'thoughtless' is the definition.
('irresponsible' can be similar in meaning to 'thoughtless')
'prisoner lies about pinching book' is the wordplay.
'about' is an anagram indicator.
'pinching' indicates putting letters inside (taking inside).
'book' becomes 'b'.
'prisoner'+'lies'='prisonerlies'
'prisonerlies' is an anagram of 'irresponsile'.
'irresponsile' going around 'b' is 'IRRESPONSIBLE'.
(Other definitions for irresponsible that I've seen before include "Nor caring about consequences" , "Reprehensibly careless" , "Showing a lack of care for consequences" , "Thoughtless" , "Negligent" .)