Lock sleeping criminal in steel bars (12)

I believe the answer is:

glockenspiel

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'steel bars' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?

'lock sleeping criminal in' is the wordplay.
'criminal' is an anagram indicator.
'in' means one lot of letters goes inside another.
'sleeping' with letters rearranged gives 'genspiel'.
'lock' going within 'genspiel' is 'GLOCKENSPIEL'.

Can you help me to learn more?

(Other definitions for glockenspiel that I've seen before include "Percussion instrument -- eg pink cellos (anag)" , "German percussion instrument" , "Musical instrument" , "Music producer" , "Percussion instrument with metal bars" .)

I've seen this clue in The Independent.

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