Collecting evidence. Forensic officer collecting a spent cartridge shell as part of evidence found at a crime scene. The ruler provided a scale for the photograph that was taken beforehand as part of a record of the crime scene. This shell was found by these bloody footprints next to a dead body with a gunshot wound. A handgun was also found. Test- firing of the handgun will allow comparison of the markings on this shell and the test shells, thus linking the shell to the handgun and indicating that it was the murder weapon. Further forensic investigation may link the gun to the murderer.