Have doubts about person thought to be guilty of a crime (7)
I believe the answer is:
suspect
'have doubts about' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for suspect that I've seen before include "Possible perpetrator of a crime" , "Distrust, have doubts about" , "Dubious" , "Person being accused" , "Have qualms about" .)