Day seven of the Delphi Murders Trial began with the testimony of Melissa Oberg. She is a former firearms examiner for the Indiana State Police. However, by the end of the day, there were only 15 jurors. One of the four alternates was excused by Special Judge Fran Gull due to a family emergency. That leaves 12 jurors and three alternates.As for the testimony, Oberg took the stand as an expert for the prosecution. She said during her career she has examined more than 66,000 weapons. She was responsible for examining the single .40 caliber Smith & Wesson Winchester cartridge found at the crime scene near the Monon High Bridge Trail. The cartridge was on the ground between the bodies of Abby Williams and Libby German. The bodies were found in woods near the Delphi bridge on February 14, 2017. The unspent bullet (or cartridge as some people call it) is significant evidence for the state's case against Richard Allen. The prosecution claims it ties Allen to the murder of the girls. Oberg testified for more than an hour during Friday's morning session. She discussed how a firearm works and explained the various parts of a cartridge. She explained to the jury that cartridge characteristics differ and why it is important. She demonstrated to the jury how a semi-automatic pistol cycles a cartridge from the time the cartridge is in the magazine, moved into the chamber, and ultimately ejected either automatically if the round has been fired or manually by someone racking the action. Oberg talked about her initial observation of the cartridge found at the crime scene. She said she could see three ejector marks on the head, three extractor marks under the rim, miscellaneous marks on the primer, and various particles in the rim around the primer. She showed a diagram of firearm parts.She said an ejector pushes the cartridge out of the magazine and an extractor pulls the cartridge out. The two internal tools work together.She showed three ways the cartridge could be ejected from the handgun.Oberg explained her exam process.Level 1 analysis involves checking the weapon's condition and what she calls class characteristics. She determines if the gun is broken or working properly. She also considers biometrics and whether any parts might be broken or missing.Level 2 analysis involves test-firing the weapon with live ammunition, and then using a comparison microscope to compare characteristics found on the cartridge/shell casing. It also includes comparing the shell casings fired from Allen's Sig pistol to the bullet found at the crime scene.Level 3 is the conclusion phase. The options are 1) identification which means the markings match 2) inconclusive which means there is not enough evidence or 3) exclusion which means the markings are not the same and do not match.Oberg testified she used a 60x magnification to observe markings on what the defense called the "magic bullet." That is the cartridge found at the crime scene. She said unique characteristics of a specific gun's surface could come from abuse, use, or corrosion. Those characteristics make unique impressions on cartridges fired by the weapon or cycled through it."Looking through the microscope is like watching a movie," Oberg said. "Pictures themselves don't represent everything we see in the examination process."Oberg compared a fired round from Allen's gun to the "magic bullet." She said there were three specific places where the markings match the cycled round found near the bodies.She said she saw three ejector marks on the head, three extractor marks under the rim of the shell casing, miscellaneous marks on the primer, and various particles in the rim around the primer.Oberg cited numerous studies in her findings. She admitted the research was not for the identical model or the extractor in Allen's pistol. Oberg said the data she collected from Allen's gun combined with research cited on the manufacturing process allows her to feel confident the .40 caliber Smith & Wesson cartridge found at the crime scene had been in Allen's gun.Defense Attorney Brad Rozzi objected to Oberg's testimony arguing the examples cited were not for the exact model of Allen's gun. Judge Gull chose not to overrule them, saying she would let the jury decide how to weigh the studies. The gun tested from Allen's house was a SIG Sauer MP226 .40 Smith & Wesson. It included: 1 Winchester .40 Smith & Wesson cartridge 1 Blazer .40 Smith & Wesson cartridge 2 MagazinesBecause Allen's gun was taken five years after the crime scene, ISP did a longevity test to see how the cartridges would hold up.Oberg said the longevity could depend on whether a person cleaned their gun with a brush that could break down parts of the gun. She examined Allen's gun and found no broken points."I was able to identify [Allen's gun] as having cycled the on-the-scene cartridge," Oberg said.But her statement came with heavy scrutiny from the defense who questioned the science behind it. Her assessment, she said, was based on four rounds fired from Allens gun and six more that were manually ejected. On cross-examination by the defense, she acknowledged the markings on cartridges manually ejected from Allens gun were not prominent enough for her to conclude if the markings matched. The defense stated it is like comparing apples to oranges.Jurors are likely going to hear from a DNA expert as testimony continues tomorrow in Delphi. It will be a shorter day court as the Saturday session is scheduled from 9 a.m. to noon.