If you want to prosecute criminals, he'll help (3)

I believe the answer is:

tec

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'if you want' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'prosecute criminals he'll help' is the wordplay.
'help' says the answer is hidden in the clue (I've seen 'helping' mean this (a helping or portion of the letters)).
'TEC' is hidden within 'prosecute criminals hell'.

'to' acts as a link.

Can you help me to learn more?

(Other definitions for tec that I've seen before include "Detective (colloq.)" , "Investigator" , "CID officer (abbrev.)" , "Busy" .)

I've seen this clue in the Evening Standard.

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