Law and ordnance

摘要

Like a criminal and his fingerprints, ev-ery gun leaves its mark on the ammunition it uses. Such traces are what Sergio Sandoval de la Pena pres over daily in Mexico City's ballistics lab. A series of dark-green circles, like the sub-woofer of a speaker, appear on his computer screen. It is a digitised three-dimensional model of a cartridge, found at the scene of a robbery this year and placed under a microscope. Checking the marks against hundreds of thousands of potential matches, Mr de la Pena concludes that the gun that ejected it was also used in a murder last year.