Witnesses must be separated during a crime scene investigation primarily to avoid collusion. When witnesses are together, there's a risk that they may influence each other's testimonies, either intentionally or unintentionally. This can lead to the sharing of misinformation, which compromises the integrity of the investigation and can distort the truth about what happened at the crime scene.
By keeping witnesses apart, investigators can gather independent accounts of the incident, ensuring that each individual’s perspective remains untainted. This practice helps maintain the reliability of witness statements, which can be crucial for resolving a case and ensuring that justice is served. Independent testimonies allow investigators to piece together a clearer and more accurate picture of the events surrounding the crime.
While separating witnesses might also relate to safety and preventing them from leaving, the main concern during the initial phase of an investigation is to maintain the integrity of their statements.