By: Don Penven, Technical Support Group
Adhesive Side Powder
Over time, many products have evolved that provide a method of fixing something, and the same is true for the tools used by crime scene investigators.
You have probably heard the old saying, “If it is supposed to move and doesn’t—use WD-40. If it moves and shouldn’t—use duct tape.” These two products have “fixed” a great many problems but one in particular—duct tape—created a whole new problem.
The criminal element has used duct tape to its advantage—it fixes something that moves—mainly the thing that moves is a hapless victim of an armed robbery, sexual assault or kidnapping. Duct tape is used to bind the victims—arms and legs—and it is used across their mouths to silence them.
Most brands of duct tape have a smooth, non-adhesive side, and this surface is relatively easy for a CSI to develop latent prints using conventional latent fingerprint powders. But, would you believe that the adhesive-side of most tapes with a tacky surface can yield better latent prints than the smooth, outer side?
For a number of years now, CSIs and crime laboratory technicians have been getting extremely useful latent prints from the adhesive-side of duct tape, packing tapes (transparent and opaque), surgical tape—virtually any tape equipped with a soft, non-drying adhesive.
But the development technique is not always a simple matter of just applying a developer of some sort. In many cases the tape is stuck to itself or mangled as it is removed from the victim. In some cases, the tape is wound on a tool or weapon in several layers also making removal difficult.
Most of the manufacturers of police field kits that provide the necessary tools to recover latent prints from the adhesive-side also include a chemical that breaks the stickiness—allowing the tape to be straightened out.
Laboratory experimentation led to the development of adhesive side development techniques. Currently two methods are available to treat the adhesive-side of most tapes equipped with non-drying adhesives:
- Adhesive-side reagent is a dry, finely milled powder (white or black for good photographic contrast). This powder is mixed with a somewhat thick surfactant solution just prior to use.
- A second method is a ready-to-use, premixed powder in solution.
1. Using the powder/surfactant combination premixed by the investigator, or using the factory mixed solution, apply the powder mixture directly to the adhesive-side of the tape using a soft bristle brush or a cotton “dauber.”
2. Allow the mixture to stand for just 10-15 seconds, and then immediately wash off the excess reagent.
If the perpetrator did come into contact with the adhesive side of the tape, which is highly likely, then the likelihood of his prints being visible is highly probable!
Once the processed tape is dry, the developed prints may be photographed (with a scale) and covered with a protective layer of regular fingerprint lifting tape.
Since research on this technique is incomplete, we are not absolutely certain as to what these reagents are acting upon:
1. It could be that the reagent is adhering to the usual, oily residue deposited by the fingertips, or…
2. It could be a thin layer of dead skin from the fingers that the adhesive pulled off, or..
3. It could be a combination of both kinds of residue.
Regardless of the why it works…the fact is that it does work, very well indeed!
Want to learn more about the exciting career of crime scene investigation…Then down load this Training Manual, “The Evidence Collection Mission.”
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