To act as a detective : search for information. (Merriam – Webster)
To search for and discover. (Merriam – Webster)
Someone whose job is to discover information about crimes and find out who is responsible for them. (Cambridge Dictionary)
A sleuth is a detective. (Collins Dictionary)
A detective. (Oxford Dictionaries)
Top ten mystery sleuths.
Crime fiction. Around the world in 80 sleuths.