Bow Street runner
FBI
FBI agent
Federal
G-man
Secret Service
Sherlock
Sherlock Holmes
T-man
detective
dick
examinant
examiner
eye
fed
gumshoe
hawkshaw
hotel detective
house detective
house dick
inquiry agent
inspector
narc
observer
operative
plainclothesman
police detective
private detective
private investigator
revenuer
scrutineer
sleuth
store detective
tec
tester
treasury agent
visitator
visitor
administrator
adviser
analyst
architect
attorney
explorer
investigations
journalist
photographer
physician
practitioner
prosecutor
psychologist
researcher
scientist
specialist
technician