What happens when ordinary people, in real-life murder clubs, set out to investigate cold cases and other crimes?

The Netflix hit Don’t F**k with Cats was based on the 2012 Montreal murder of thirty-three-year-old Lin Jun by his porn-star boyfriend, Luka Magnotta. Previously Magnotta had anonymously posted videos of himself killing kittens. This spurred horrified Facebook sleuths into working tirelessly to uncover his identity and location.

In other cases featured, a self-taught forensic artist uses computer software and coroners’ photographs to show what victims looked like when alive.

A mother, who swore at her daughter’s graveside that she would get the gang who had sprayed her car with bullets, fulfils her promise, even if it takes her fourteen years to catch the last killer.

Websleuths matched the IP address of a suspicious contributor to a lottery-winning victim’s financial advisor, which led to his body being found beneath a newly poured concrete slab in his advisor’s boyfriend’s garden.

Sometimes citizen sleuthing goes wrong, though, with innocent people being targeted, or accused of crimes they haven’t committed, with tragic results.

The real-life version of Richard Osman’s The Thursday Murder Club is grittier, with intrepid amateur investigators delving into truly gruesome unsolved crimes in pursuit of justice.