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.
They do know how it works: it detected a pattern in the difference between fingers and checks that.
Also this would usually not be needed explained to a jury. If they have the suspect in custody they can just check their fingerprints directly.
That’s again 2 fingerprints to compare: one from the crime scene, and one from the suspect.
Yeah but comparing a fingerprint to a finger is a simpler test than comparing a fingerprint to another fingerprint and checking if they may be two fingers from the same person.