How accurate is shell casing analysis?

Firearms expert would stake his life on its accuracy

Nelson Welch is an independent firearms forensics expert. In 2008, "48 Hours" asked him 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.

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

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