A secure crime scene

The instant the police arrive at the scene of a crime a list of procedures are put into place and strictly adhered to. The reason for this is simple: crime scenes may look barren, but in fact they are bristling with evidence that connects a crook with the crime. It’s vital that clues are not disturbed, contaminated, or lost – failure to put these practices into place can jeopardise the entire case. 

The first action is to assess the extent of the scene and cordon the area off - whether it’s a single room or an entire street. All evidence must be preserved as it was found. Also, it’s crucial that the number of people entering the scene is kept to a minimum since anyone entering (yes, even detectives) can introduce confusing trace matter. To make allowances for this, officers set up a record of anyone entering and leaving the crime scene.

Officers then determine whether the site is a primary or secondary crime scene - whether the crime actually happened here or whether it was a place the suspect moved to once the crime had been committed. They also try to establish the suspect's entry and exit points.