Officer damages murderous computer (7)
I believe the answer is:
marshal
'officer' is the definition.
(I know that marshal is a type of police officer)
'damages murderous computer' is the wordplay.
'damages' becomes 'mars' (marring is a kind of damaging).
'murderous computer' becomes 'HAL' (HAL 9000 from 2001 A Space Odyssey).
'mars'+'hal'='MARSHAL'
(Other definitions for marshal that I've seen before include "Arrange; senior officer" , "US federal officer" , "Maybe a bulldog" , "Mobilise -- US law-enforcement officer" , "Sports event official" .)