Electron Microscopes Can Reveal Filed-Off Serial Numbers

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To make it difficult for law enforcement to trace stolen cars or weapons, thieves will usually grind off their metal vehicle identification numbers or serial numbers. And while techniques for trying to recover those numbers do exist, they're not as accurate as a new method developed by researchers at the National Institute of Standards and Technology—or NIST—that uses a scanning electron microscope to detect imperfections in the metal's crystalline structure.

Part of what gives metal its strength is that its atoms are arranged in a well-organized and highly patterned crystal structure. But the act of stamping a serial number onto metal can damage that crystal structure deep into the material—well below the surface area that thieves will typically grind away to erase the stamped digits.

As an electron microscope scans a beam of electrons across a metal surface that has been ground down to erase a serial number, the reflections can reveal what the crystal structure deep into the material looks like. Using software to differentiate the quality of the crystal pattern can then reveal damaged areas below the surface, which in turn can be used to re-generate serial numbers that have been erased.


The quality of the results achieved from the new recovery technique are likely to allow it to be used as forensic evidence at a trial, but unfortunately in its current form the new approach is very time consuming. A single technician needs about three full days to recover an 8-digit serial number, which would have labs backed up for years. But the NIST researchers believe that improvements made to the software, as well as more detailed scans, could reduce the recovery time to about an hour, which could help make the new technique a viable tool for forensic investigators. [National Institute of Standards and Technology via Slashdot]