Crime ultimately without motive (7)
I believe the answer is:
treason
'crime' is the definition.
(I know that treason is a type of crime)
'ultimately without motive' is the wordplay.
'ultimately' says to take the final letters.
'motive' becomes 'reason' (reason is a kind of motive).
The last letter of 'without' is 't'.
't'+'reason'='TREASON'
(Other definitions for treason that I've seen before include "Crime of disloyalty" , "Disloyalty (to one's country)" , "Stare on (anag.)" , "Criminal attempt to overthrow a government" , "Deliberate act of betrayal" .)