Sherlock Holmes could look at a gun shell and know exactly what went down. The firearm? The shooter's stance? The culprit? All revealed with a glance. In the real world, using a shell to solve a crime is a painstaking, and often unsuccessful, process. Investigators may be able to match a bullet with a gun type, but that doesn't necessarily lead to the person who shot it. Useful fingerprints are rare, and the heat of firing a weapon can destroy DNA evidence.