False witness found entering Mali, arrested (4)
I believe the answer is:
liar
'false witness' is the definition.
(thesaurus)
'found entering mali arrested' is the wordplay.
'found' indicates the answer is hidden within the clue.
'LIAR' can be found hidden inside 'entering mali arrested'.
(Other definitions for liar that I've seen before include "Story teller?" , "One supplying pork pies" , "Untruthful person (Billy in Schlesinger film)" , "Teller of untruths" , "Fabricator" .)