Performance Evaluation and Utility Assessment of Magneto-Optical Sensor Technology for Detecting and Visualizing Obliterated Serial Numbers in Firearms

摘要

In the United States, firearms manufactured after 1968 must contain a serial number somewhere on the metal frame. Each number is unique and typically stamped into the metal. During the stamping process, the crystalline structure of the metal is deformed and compacted below the identification number. When criminals destroy the serial number (using a variety of filing, grinding, and peening techniques) to avoid tracing of the firearm to its owner, the serial number may not be visible to the naked eye, but may still be recoverable. Recovery of the obliterated serial number greatly depends on the material used in the manufacturing of the firearm and on the depth of the obliteration. Over the years, a number of techniques have been developed to detect and restore obliterated serial numbers in firearms. Current techniques fall into one of two categories: destructive and nondestructive. In destructive methods, the most commonly used technique is chemical etching. Restoration by this technique requires extensive sample preparation, the appropriate selection of etchants, and extreme care during etching of the specimen. In non-destructive methods, such as magnetic particle inspection (MPI), the original state of the specimen is preserved. Because of this preservation of material, non-destructive methods are generally preferred by examiners. However, nondestructive methods are extremely messy and suffer from low sensitivity.