Hand tool to cool detective on crook's case (7)

'hand tool' is the definition.
(icepick is a kind of hand tool)

'cool detective on crook's case' is the wordplay.
'cool' becomes 'ice' (icing is a kind of cooling).
'detective' becomes 'PI' (private investigator).
'on' is a charade indicator (letters next to each other).
'case' suggests removing the centre.
'crook' with its centre taken out is 'ck'.
'ice'+'pi'+'ck'='ICEPICK'

'to' acts as a link.