Thursday, December 18, 2008

Luminol Photography

Luminol is a blood visualizing agent that is commonly used in crime scene investigation because it produces a chemical reaction with hemoglobin causing luminescence (glowing) wherever blood is present. It is usually used as a final step because it normally does not produce significant detail for pattern identification but has tremendous value as a locater of blood. Luminol is applied by spraying and can be a great resource when you are just trying to find traces of blood but don’t have any idea where to begin looking.

In the past, Luminol was only useful for finding blood traces because it would destroy DNA making any identification of the blood that you found improbable. This is no longer the case as there are certain variations of Luminol that are available that do not destroy DNA. BlueStar® Forensic was developed in 2000 and has become my personal favorite. It does not destroy DNA, it produces a stronger and longer-lasting luminescence, and it has a longer working life. While I still use it as a last step, it can often help me find the DNA evidence that I need.

Of course, everything needs to be documented as thoroughly as possible. This includes photography of the luminescence which is a tremendous challenge. The preferred steps for photographing Luminol have been to place the camera on a tripod, remove or turn off the flash, set the focus manually, use a remote shutter release, and use an automatic setting on the camera if available. This also requires that the ambient light in the area is restricted as much as possible. I carry a large roll of black plastic to cover windows and doors for this purpose. With standard Luminol, the photographs were never very useful and rarely showed any of the luminescence that I was able to see at the crime scene. Switching to BlueStar® Forensic made it possible to produce better photographs due to the increased intensity and duration of the luminescence, but the background was not visible. What I wanted was to photograph the luminescence as well as the surrounding area so that I could effectively document not only the presence of luminescence, but its location as well.

I have found that if there is some ambient light, Adobe Photoshop® can be used to enhance the original image. First, make a duplicate layer to avoid working on the original image. Then from the top menu bar, select Image > Adjustments > Auto Levels, some improvement to the background can be produced without reducing the quality of the luminescence. While this method tends to produce truer colors than other methods, it still does not clarify the background to my satisfaction in most cases and Photoshop can be a difficult program to master. If you choose to use this method, remember to save a copy of the file for court purposes and document each step in a report so that you can reproduce the results.

The problem with photographing Luminol is that cameras require light to operate but Luminol requires darkness to be visible. In order to illuminate the background, some light is required. Since Luminol produces a blue luminescence, the background can be illuminated with a different wavelength using an alternate light source. I have only recently begun to experiment with this technique, but I am gaining a preference for ultraviolet because it seems to produce a great deal of contrast to the blueish glow of the Luminol. When learning this technique, keep in mind that the amount of ultraviolet light required is very minimal since the shutter speed is going to be very slow. If you have a digital camera, take several pictures to help determine what the best direction and distance of the light source will be prior to applying Luminol.