Spotted killer's desire to break into laugh (5)
I believe the answer is:
hyena
'spotted killer's' is the definition.
(most hyenas are spotted)
'desire to break into laugh' is the wordplay.
'desire' becomes 'yen' (yen can mean a longing or desire).
'to break into' indicates putting letters inside (inserted letters break into the word).
'laugh' becomes 'ha'.
'yen' placed inside 'ha' is 'HYENA'.
(Other definitions for hyena that I've seen before include "Flesh-eating dog with eerie laugh" , "African carrion-feeder" , "Carrion-eating, dog-like animal" , "Wild mammal" , "Dog-like animal with laughter-like howl" .)