Curiosity shown by soldiers in trial cases (8)
I believe the answer is:
interest
'curiosity' is the definition.
(interest is a kind of curiosity)
'soldiers in trial cases' is the wordplay.
'soldiers' becomes 're' (Royal Engineers).
'trial' becomes 'test' ('test' can be a synonym of 'trial').
'cases' is an insertion indicator.
'in'+'test'='intest'
're' going into 'intest' is 'INTEREST'.
'shown by' is the link.
(Other definitions for interest that I've seen before include "Money paid by borrower" , "Concern - money accruing" , "Hobby" , "Significance" , "Deposit account gain" .)