Which evidence is critical in tracing gun ownership?

The identification of serial numbers on firearms is critical in tracing gun ownership because these numbers serve as unique identifiers assigned by manufacturers to each firearm. The serial number allows law enforcement and investigators to track the history of a firearm, including its sales and transfer records, which can link it to previous ownership or criminal activity. When a firearm is recovered at a crime scene, the serial number can be checked against databases, helping authorities to determine the original purchaser and any subsequent transactions. This traceability is vital for investigations into gun crimes and for understanding the flow of firearms in the public domain.

Other options like barrel length, type of gunpowder, and color of ammunition do not carry the same level of identification and cannot conclusively establish ownership or history of a firearm. While these features may provide additional information about the firearm, they do not serve as reliable means for tracing back to the original owner as effectively as serial numbers do.