Crazy graduate turned murderer (6)
I believe the answer is:
maniac
'crazy' is the definition.
(I've seen this before)
'graduate turned murderer' is the wordplay.
'graduate' becomes 'ma' (abbreviation for Master of Arts).
'turned' says the letters should be written in reverse.
'murderer' becomes 'cain' (Cain who killed Abel).
'cain' backwards is 'niac'.
'ma'+'niac'='MANIAC'
(Other definitions for maniac that I've seen before include "Psycho" , "Lunatic or person behaving wildly" , "Can aim (anag.)" , "Psychopath" , "Nutter" .)