Which technique is primarily used to secure biological evidence at a crime scene?

Using gloves and evidence bags to prevent contamination is the primary technique employed to secure biological evidence at a crime scene. Biological evidence—such as blood, saliva, or other bodily fluids—can easily be compromised by DNA transfer or degradation if not handled correctly. By wearing gloves, investigators prevent their own DNA from contaminating the evidence, which is critical for maintaining the integrity of the sample. Additionally, placing the evidence in specialized evidence bags helps to protect it from environmental factors such as moisture and dirt, as well as prevents further contamination from external sources.

This method is essential for ensuring that any biological evidence collected can be reliably analyzed in a laboratory setting, thus playing a crucial role in the overall investigative process. Other methods like photographing and sketching, while important for documentation, do not secure the biological evidence itself. Collecting multiple samples is beneficial, but without the proper precautions of handling and packaging, those samples could still be rendered unusable. Interviewing witnesses, while helpful for gathering information, does not have a direct role in the physical securing of biological evidence at the scene.