Gary works as a police officer. He has just arrived at a crime scene. He has secured it with ropes (cordoned it off) so that people do not enter the scene. What could be Gary's purpose?

to prevent contamination of evidence

Explanation:

As a police officer, it is the responsibility of Gary to ensure that he appropriately protect, preserve, secure, and expectedly collect evidence. To be able to do this adequately, one of the ways is to secure the crime scene with ropes (cordoned it off) so that people do not enter the scene. The main purpose of this is to "prevent contamination of evidence."