An "amateur sleuth" refers to someone who investigates and solves crimes without being a professional detective or law enforcement officer. Full definition
As the movie begins, the audience learns that Sadie and McKayla have been trying to boost their online profile by acting as amateur sleuths in pursuit of a local serial killer. (scene-stealers.com)
This started a month ago, and he's managed to get the first book of my series properly categorized and in the top 100 of Amateur Sleuths for over three weeks. (elizabethspanncraig.com)
Suspicions were first raised by amateur sleuths on a cryptocurrency forum on Reddit, who wrote that Confido's founding team appeared to be fake people with dubious profiles. (inc.com)