Hold the murderer, not tied up, inside (7)
I believe the answer is:
contain
'hold' is the definition.
(synonyms)
'murderer not tied up inside' is the wordplay.
'murderer' becomes 'cain' (Biblical figure).
'tied up' is an anagram indicator (letters get tied or tangled up).
'inside' indicates putting letters inside.
'not' with letters rearranged gives 'ont'.
'cain' going around 'ont' is 'CONTAIN'.
'the' acts as a link.
(Other definitions for contain that I've seen before include "Accommodate" , "I cannot (anag) - hold back" , "Carry" , "Keep within limits or have within" , "keep within bounds" .)