Describe the proper methods for collecting and documenting firearm evidence at a crime scene, ensuring safety and preservation of ballistic markings.

Collecting firearm evidence requires strict adherence to safety protocols and careful documentation to preserve its evidentiary value, particularly ballistic markings which are unique to a specific firearm. Before handling any firearm, it must be treated as loaded until proven otherwise. Safety is the paramount concern. Prior to collection, the firearm's condition (e.g., cocked, safety on/off, magazine inserted) should be documented in detail, including photographs and notes. To render the firearm safe, the magazine should be carefully removed (if applicable) and the chamber should be cleared of any live rounds. These rounds should be collected as separate pieces of evidence. The firearm should then be secured using zip ties or evidence tags to prevent accidental discharge during handling and transport. When handling the firearm, it should be gripped on areas that are least likely to contain fingerprints or ballistic markings, such as the checkered portions of the grip or the trigger guard. Avoid inserting anything into the barrel, as this could damage the rifling and alter the ballistic markings. The firearm should be packaged in a rigid container, such as a cardboard box or a plastic gun case, to prevent damage during transport. The container should be clearly labeled with the case number, item number, date, time, and the collector's initials. Ammunition and magazines should be packaged separately from the firearm. Each cartridge should be placed in an individual container, such as a small plastic bag or a pill bottle, to prevent damage to the bullet or casing. The containers should be labeled with the same information as the firearm. Cartridge casings found at the scene should be collected carefully, using gloved hands or clean tweezers. Avoid scratching or damaging the casings. Each casing should be placed in a separate container and labeled. Trajectory analysis may be needed to determine the path of bullets. Trajectory rods and lasers are used to determine bullet paths. Photographs should be taken of the bullet holes or impacts, and the angles and distances should be measured and recorded. All firearm evidence should be documented thoroughly. This includes creating a detailed inventory of all items collected, as well as documenting the location where each item was found, the condition of the item, and the steps taken to collect and preserve it. A chain of custody form should be completed to track the possession of the evidence from the time it is collected until it is presented in court. For example, if a handgun is found at a crime scene, the officer would first document its condition, then carefully remove the magazine and any rounds from the chamber, package the gun in a gun case, and label the case with all relevant information. The ammunition would be packaged separately. The officer would then complete a chain of custody form, detailing the collection and packaging process. Photos and measurements of the location and gun itself would also be added to the crime scene documentation.