Material concealed by this criminal (5)
I believe the answer is:
scrim
'material' is the definition.
(I know that Scrim is a type of material)
'concealed by this criminal' is the wordplay.
'concealed by' says the answer is hidden in the clue.
'SCRIM' can be found hidden inside 'this criminal'.
(Other definitions for scrim that I've seen before include "Open-weave muslin fabric" , "material" , "A loosely-woven cotton fabric" .)