"Law officers and detectives take special care to preserve crime scenes, exactly as they find them, because evidence is fragile, and clumsy feet and prying hands can easily destroy it. Without evidence, it may be impossible to solve a crime and catch the villains who carried it out."
"The more people who visit a crime scene, the more chance there is of destroying evidence. So an important priority is to keep away journalists, curious neighbours -- and even other officials whose visit is not absolutely essential."
"Once the crime scene is taped off, there are other simple, but essential precautions that officers need to take. They must not eat, drink or smoke, because these activities leave traces that may later confuse investigators."