EVANSVILLE, Ind. (WEHT)– One piece of evidence cracked the Delphi murder case wide open. Police say a 40-caliber bullet was found near the bodies of teenagers Abby Williams and Libby German connects Richard Allen to the Delphi murders. But how did investigators connect that bullet to Allen’s gun? The Indiana State Police Lab in Evansville has similar equipment to what police in Central Indiana used to find that link.

Mitzi Templeton is a forensic scientist at Forensic Firearm Investigation Lab and showed us the process of how they found a match.

“When I do an identification, there are some that are just beautiful. You can take a picture of it and see that it is an ID,” she says.

But sometimes, it is not that evident. Each gun leaves different markings, even those made on an assembly line next to each other. These more difficult cases require a ballistics analysis, beginning with a test fire.

“We’ll do a function exam to make sure it operates as designed, retrieve those test fires, and put it on a comparison scope,” she says.

Templeton puts the bullet under two microscopes that are connected by an optical bridge. It shows two sides, the evidence, and the test fire, separated by a dividing line. They can compare the evidence and the test fire together by using a split screen.

“When we are looking at those, we want to see if there are identical marks,” Templeton says.

There are spiral impressions inside the gun barrel, called rifling. When the gun is fired, these grooves cut into the bullet.

“As the bullet goes down that barrel, it is squeezing up against that barrel and it creates these impressions,” she says.

Templeton then looks for impressions that align, between the evidence and the test fire. If they are the same, then it is a match.