Which of the following is a common source of physical evidence?

Biological samples from the scene are considered a common source of physical evidence because they provide tangible, physical materials that can be collected and analyzed in a laboratory setting. These samples can include blood, saliva, hair, or other bodily fluids, all of which can be crucial for forensic analysis. They can help establish connections between the suspect, the victim, and the crime scene, often leading to critical insights into the crime being investigated.

In contrast, witness testimonies are subjective accounts and do not constitute physical evidence, as they rely on human memory and perception. Surveillance videos, while they can capture physical events, are more often viewed as recordings of incidents rather than direct physical substances that can be analyzed separately. Police reports, though essential for documenting the case and providing context, also do not serve as physical evidence themselves; they summarize findings and observations rather than providing material that can be examined in forensic investigations. Therefore, biological samples stand out as a common source of physical evidence in criminal investigations.