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Magneto-Optical Sensors Bring Obliterated Serial Numbers Back to Life

NCJ Number
NIJ Journal Issue: 275 Dated: May 2015 Pages: 1-1
Date Published
May 2015
1 page
Publication Series
This article describes progress to date of a NIJ-sponsored project that is determining whether a new system that combines magnetic fields, polarized light, and a special sensor is better than the traditional method for recovering and reading obliterated serial numbers.
The new method uses magneto-optical (MO) sensor technology to nondestructively detect and visualize serial numbers that have been scratched, ground, chiseled, or otherwise removed from firearms. Thus far, the project researchers report that although this new system isn't perfect, compared to the current nondestructive method used in most crime laboratories, i.e., magnetic particle inspection (MPI), MO sensor technology is "slightly more sensitive, sees a little deeper, is not as messy, and requires a little less work." The project, which began in 2011, has completed the first phase of research, which involved testing the sensors on flat, smooth surfaces. The project is currently testing some of the 2,000 firearms in the Johnson County Sheriff's Office (Missouri) crime laboratory's reference library. This article notes that both the MO Sensor technology and the standard MPI method use strong magnetic fields to reveal obliterated serial numbers, which requires that the firearms be made of a magnetic material. For weapons made of nonmagnetic materials, crime laboratories must still use chemical etching, which uses strong acids and typically reveals a serial number for only a few moments before possibly destroying it. Regarding cost considerations, phase two testing has discovered that laying a sensor directly on a firearm avoids the expensive viewing system, and using fragments of broken sensors can also reduce costs, providing they are large enough to cover an obliterated area. The collection of the final data from phase two will soon be completed and a final report published within several months.

Date Published: May 1, 2015