How to collect physical evidence in inclement weather
We do not get to pick our crime scenes. Instead, our crime scenes select us through random chance and whatever crazy schedule we might be working. Crime Scene Investigators must play with the hand we were dealt with by the suspect(s) and random chance. Crime scenes are presented to us in the extreme cold, extreme hot, pouring rain, snow, and the occasional beautiful day if we are lucky. We have to adapt to the circumstances at hand. If the weather continues doing what it is doing before, during, and after your arrival on the scene, then your conditions remain relatively static. That is to say that a crime scene that you pulled upon in the rain was already wet, the evidence was already wet and evidence loss as a result of the rain, such as DNA or small blood spots, has likely already occurred. Processing the scene will require protecting your equipment from the weather as you document the scene and collect your wet evidence that will need to be dried upon return to your laboratory. The real problem for us is when we pull up on the scene of an outdoor event and the weather is about to make a significant change. This is when you have to think fast. I once had a scene where I pulled up to an outdoor shooting just as the sky opened up with a massive downpour. I literally got there in time to see several cartridge casings floating down the gutter heading toward the drain. I had enough time to slap a pair of gloves on and scoop them out of the gutter just before they were gone forever. The good news was that they were recovered and preserved. The bad news was that there were no photographs, measurements, or other documentation of these casings. I would still say that was a win given the changing conditions that were beyond anyone’s control.
Two other scenes come to mind where the scene processing was well underway when the weather started to change when there was no forecast for the weather change. Both involved small low-velocity blood drops that were believed to be suspect blood. In one instance, a light rain starting moving in. In the other case, it started to snow. Each of these had to be dealt with differently. In the case of the rain, the suspected blood droplets immediately became priority number one. Once they were collected, we moved on to electronic items like phones that were on the ground getting wet. Then on to items that would absorb the moisture from the rain like the bloody clothing cut from the victim during lifesaving efforts. Finally, the remaining items were collected. Then, of course, the rain stopped. Just the way it works sometimes. In the scene with the snow, we took a different approach. We were able to place markers overtop of the minute blood spots to protect them from the snow. Then we could continue processing the scene through our normal protocols. In this example, that worked great; however, that is not always a good solution. Shoe impressions and tire tracks in the snow can be easily destroyed by additional snow. The natural thought would be to cover these impressions with something like a cardboard box to prevent them from being filled in by the additional snow. However, this may not work out as well. At night, you are more likely to get away with this as a reasonable technique to buy some time, but during the day time, even on a cloudy day, the brown cardboard is likely to absorb enough heat from the sun to melt away any impression that may be under the box. As a result, you always have to evaluate and prioritize your evidence documentation and collection. You do not want to take a chance of sacrificing your evidence in exchange for good documentation. Ideally, we always want good evidence documentation and proper collection techniques that avoid potential cross-contamination and preserve any trace evidence that may be present such as friction ridge detail or hairs and/or fibers. However, if the weather only gives you time for documentation or collection. The choice is clear. Always be sure to record your reasons for your decisions and circumstances for breaking your standard protocols for documentation in your notes or your evidence management software. You will have to be able to defend yourself later in the courtroom as to why you made the decisions that you made when you made them.
Upon return to your office, be sure to continue the process of protecting the evidence. If the evidence is wet from either blood or weather, be sure to place the items in an appropriate evidence drying cabinet until completely dry. Make sure that evidence that should not be commingled is kept completely separate to avoid cross-contamination. Be sure that you are properly documenting the chain of custody of your evidence in your evidence management software so that you can easily reproduce your chain of custody to show that there was never an opportunity for cross-contamination to have occurred.
Weather can create miserable and challenging conditions for Crime Scene Investigators. We have to improvise, adapt, and overcome in order to optimize our evidence documentation and collection. Advanced planning is always an asset such as having pop-up tents or tarps to protect our scenes. However, the best tool we have is our experience, the experience of those who have been there before us, and our quick thinking. We have to make the best of the circumstances in which we are working while protecting ourselves, our equipment, and of course, our evidence.