Transient evidence

Certain aspects of a crime scene may manifest themselves only for brief periods. For instance, the distinctive smoke and odor an incendiary device emits may be evident only within the first few minutes. Those arriving on the scene later, when the blaze is fully fueled by the structure itself, might perceive no indicators of suspicious origin, and indeed might not search for such a device among the debris.

Other examples include: the heat of a gun barrel, indicating it had been recently fired. The color of a bloodstain, indicating its freshness. The absence of transient environmental evidence can also be evidentiary, as in the case of odors associated with decomposition. If a skeletal body is found within the confines of a frequented space (such as in a closet in a public bar), the fact that no one complained about the smell during putrefaction is a strong indicator that the body has been relocated.

Not all scenes can remain preserved during the course of an investigation. A vehicular incident, for example, must often be quickly cleared from the road. An exterior scene can be promptly compromised by weather. Sometimes aspects of the scene are intentionally destroyed in the process of investigation: one might, for instance, break down a locked door to discover what is on the other side, destroying a pattern of blood spatters on the door in the process.

In all such instances, the advent of photography has become invaluable. Immediate and extensive photographing of a scene is often the only means of preserving transient contextual evidence, which is why photographic documentation, in standard protocol, takes precedence to all other steps of investigation (subsequent to securing the scene). Investigators are encouraged "to not hesitate to photograph something which has no apparent significance at that time - it may later prove to be a key element in the investigation." .^[3]