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How accurate is the analysis of spent shell casings?

Firearms expert says he would stake his life on its accuracy

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In 2008, "48 Hours" asked Nelson Welch, an independent firearms forensics expert, to help us understand how and why Albuquerque Police investigators were so confident that a shell casing found inside the home of then-murder suspect Ron Santiago was a direct match with four shell casings found at the scene of a double murder.

"48 Hours" took Welch to a gun range where we fired bullets we could use for analysis.

In the video clip below, Welch was passionate about his ability to spot a match and gave us insight into this sub-specialty of matching shell casings: