How CSI processes wet surfaces for hidden fingerprints.
It took more than 5 hours when an observer police patrol discovered that the car was being used in an armed robbery. The vehicle description, color, and license tag correspond to a radio bulletin broadcast earlier during the “cemetery change”. The vehicle was also declared stolen the day before.
In short, the crime scene investigation team arrives at the scene of the incident and makes a quick visual inspection of the vehicle's appearance. Of particular interest are areas that may have affected previous passengers. Using flashlights at different angles, CSI studies the appearance for possible hidden prints. They can see or not see. In the end, hidden printing means that which is not visible.
Processing for hidden prints through the interior of the car will be common, but the appearance is a special problem - it is soaked wet, and the constant rain continues to fall.
Hidden fingerprints developed by powders are generally the first choice for researchers working in crime scenes, and in this case auto crimes. To treat the areas outside, the crime specialist will apply a specially prepared powder using a fiberglass or animal (camel or white) hair brush. But using this dry powder on a wet surface will only lead to confusion, and any detail of the fingertip will be erased.
The investigators have only two options left:
1. Wait until it stops raining and do not let the machine dry or
2. Find other ways to handle the car for hidden prints, despite the rain
For option 2. above, many CSI teams will use a recipe that has become known as Small Particles Reagent or simply SPR.
Unlike many other latent technologies for print design, such as silver nitrate and nihydrin, which was originally used for other scientific purposes, SPR investigated specific studies and experiments to find means for developing hidden prints on wet surfaces.
The original SPR formula consists of very finely ground black powder - molybdenum disulfide, as well as liquid detergent and water. This mixture, when sprayed on a vertical or almost vertical surface, tends to pass down. If hidden prints are present, the liquid suspended black powder is attached to the residual moisture of the latent prints, thereby making the visible structure of the print ridge visible.
SPR Dark works fine on light surfaces, but is of little value if the surface is painted black. The fact that the researchers came to the following was a formula using finely ground white powder-titanium dioxide and the same mixture of water-detergent. SPR Light and SPR Dark are in many places to investigate crimes.
In recent years, a third formula has been developed that will help in latent restoration of printing from multi-colored backgrounds. This mixture is fluorescent - it glows in the dark when long-wave ultraviolet light is used. Like his colleagues, SPR UV uses the same vehicle for detergents.
SPR UV then fills an identical void in formulas that provide CSI with enough variety to cover most wet surface conditions.
The use of the SPR formula is simple - it is applied using a spray bottle. The mixture is sprayed onto the surface above the area suspected to contain latent prints, and is allowed to flow over the surface. The solution also lends itself to tray design.
While its main purpose is a latent imprint on wet surfaces, it can be used on a non-porous surface - wet or dry.
Once the latent prints are developed, they should be immediately photographed, because they are quite fragile, and when they are wet, they can be very easily lifted with tape, hinges, etc.
