Thorough investigation (5)
I believe the answer is:
probe
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">thorough investigation</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for probe that I've seen before include "Explore, examine" , "Inquiry" , "sound" , "Examine searchingly" , "Intrusive device" .)