DELPHI, Ind. (WISH) — Testimony today in the trial of a man accused of killing two Delphi tennagers in 2017 centered around “tool marks” and the evidence a firearm leaves on a fired and un-fired cartridge.

The State called Melissa Oberg, a former forensic firearm examiner for the Indiana State Police. She resigned that position in 2013, but before that worked on the Delphi case. She told the jury she looked at cartridges, did function exams on firearms and did tool mark examinations.

In today’s testimony, Oberg told the jury that she test-fired a new cartridge similar to the one found near Abby and Libby’s bodies in 2017. She said that the test cartridge showed similar “tool marks” to the un-fired cartridge found at the crime scene.

Tool marks are caused by the harder metals inside a firearm coming into contact with the softer metals that make up a cartridge.

A cartridge is how an unspent bullet is normally referred to. The casing is ejected when a gun fires the bullet. When a firearm is “cycled”, the entire cartridge is ejected from the gun without the bullet being fired. “Cycling” the gun is also sometimes referred to as “racking” and makes a distinctive sound.

Allen’s gun was a 40 cal. Sig Sauer. Prosecutors say Allen used the gun to move the girls from the bridge to the area where they say the girls were murdered. Prosecutors say Allen “cycled” the gun at some point, causing the cartridge to fall to the ground between the bodies where it was later found by investigators.

News 8’s Kyla Russell reports that a caveat of Oberg’s testimony was that the test cartridge was actually fired, while the cartridge found at the crime scene was not.