Improving technique increases murder rate (10)

I believe the answer is:

upskilling

'improving technique' is the definition.
(improving one's skills)

'increases murder rate' is the wordplay.
'increases' becomes 'ups' (upping is a kind of increasing).
'murder rate' becomes 'killing' (I can't justify this - if you can you should believe this answer much more).
'ups'+'killing'='UPSKILLING'

I've seen this clue in The Times.

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