Final answer:
At a crime scene, one must prioritize the preservation of evidence, document meticulously, and restrict access only to authorized personnel. For evidence like a gun found in water, proper retrieval, preservation, and adherence to forensic protocols are essential to maintaining the integrity of the evidence.
Step-by-step explanation:
When approaching a crime scene, the first thing to teach your new partner is the importance of preserving the scene to prevent contamination of evidence. This process includes setting up barriers, documenting the scene with notes, photographs, and sketches, and only allowing authorized personnel to enter.
When handling a gun found at the bottom of a river, it's critical to maintain the chain of custody and preserve any forensic evidence. This means documenting its exact location, photographing it in situ, wearing gloves to prevent fingerprints contamination, and carefully retrieving the gun without disturbing potential fingerprints or other trace evidence. The firearm should then be placed in a container with enough water from the river to prevent any biological evidence from drying out and degrading.
It's essential to keep in mind that all evidence, especially firearms, must be processed according to proper forensic protocols. This involves considerations around ballistics, DNA, and residue analysis, and cooperating with forensic experts who specialize in these areas.