Dispatched casually: certainly laid back (5)

I believe the answer is:

offed

'dispatched casually' is the definition.
(off can mean to kill or dispatch)

'certainly laid back' is the wordplay.
'certainly' becomes 'deffo' (short for definitely).
'laid back' is a reversal indicator.
'deffo' written backwards gives 'OFFED'.

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app