From "Law and Order" to "CSI," not to mention real life, investigators have used fingerprints as the gold standard for linking criminals to a crime. But if a perpetrator leaves prints from different fingers in two different crime scenes, these scenes are very difficult to link, and the trace can go cold.
This was known long ago, but its very very very improbable to have two people with the same fingerprints in the same area, let alone be part of a crime/ a suspect.
Its just like DNA, its not perfectly unique but the combination of stuff is what gets you arrested.
Ok, so caveat: this trivia is a few decades old in my head… but I thought there was a higher chance of similar fingerprints if there’s a genetic relationship? Which meant that mistaken identities were more common because of socio-economic and geographic factors for relations.