Fingerprints are perhaps the most common physical evidence used to identify victims and offenders and are considered one of the most valuable types of evidence to be recovered during a criminal investigation. With few exceptions, everyone has fingerprints and not one print has ever been known to duplicate another fingerprint. Therefore it is possible to positively identify someone with just one print.
Prints come from the surface of each friction ridge of our fingers, palms, toes, and feet, which have minute pores that exude perspiration. The composition of our perspiration is approximately 98.5 to 99.5% water and approximately .5 to 1.5% solids like chlorides (salts), urea and amino acids. When these print-bearing areas come in contact with certain foreign surfaces, they leave a detailed outline of the ridge impression called a "latent print."
Types of Prints
The following are three of the most common types of prints you'll come in contact with as an Underwater Criminal Investigator:
1. Latent prints - These are usually invisible or partially invisible and are comprised of water (perspiration) and solids. By having a good strong light source and utilizing a cross or side lighting technique, you can often make such a print visible. When developing latent prints, you must use powder or other chemicals so that the latent ridge detail may be photographed or lifted for preservation.
2. Patent prints - These are usually made from ridges coming into contact with foreign material such as blood, grease, or paint and are usually visible. Depending on the material, these prints are usually not preserved by lifting but by having them photographed. It is essential to get hold of someone qualified and capable of photographing such prints before they are destroyed. Quite often the investigating department has a crime scene photographer trained and very capable of handling this type of preservation.
3. Plastic prints - These are prints impressed in any soft medium such as putty, soft candle wax, or soap.
Usually they are also preserved through photography but can sometimes be preserved through careful recovery of the medium in which the print was left.
When considering whether or not prints are to be lifted or otherwise recovered from an area, the following should be taken into consideration:
1. Type of surface (like glass, metal, or paint-covered surfaces)
2. Time submerged
3. Recovery (lifting) technique
Although submersion of an item does not enhance the possibility of recovering readable prints, it does not eliminate the possibility either. Studies have shown that fingerprints can be recovered from certain surfaces (metal, glass, and plastics) after being submerged for days. For this reason, every item recovered from the water should be checked for prints if the item, when found on the surface, would normally be processed for prints. The exception to this practice would be if the item's condition made it obvious that no prints would be found.
Who's going to do the processing?
A little knowledge and a lot of common sense are needed in determining whether or not the evidence will be processed for prints by the investigating officers or by the lab. Some suggestions to help you with this are:
1. If the evidence was used in a serious crime, such as murder, assault, or robbery, and the item is a gun or knife, it would be best, if at all possible, to have a laboratory technician conduct the examination.
2. If the item is the size of a car, a laboratory examination might be impractical. The original investigating officer or someone from his department, such as a crime scene technician, should then do the latent print processing.
3. Quite often common sense tells you there is no need to process for prints because of the length of time the item was submerged and the general overall condition of the item.
The longer the item is submerged, the less chance you have of recovering any prints. However, if the print is protected in some way from direct water exposure, the print will maintain its structure longer than one exposed to the ambient water, where the friction created by direct water contact will wash away the print much faster. Water is an excellent solvent. This is illustrated by the contrast between the prints left on the inside rearview mirror of an automobile and the prints left on the side view mirror mounted on the exterior of the driver's door. The prints on the inside mirror would be protected from moving water and therefore last longer.
Remember - Given enough time, water will even dissolve glass.
If you're asked to assist or process the latent print
It is rare that an Underwater Criminal Investigator would be processing the evidence at the water's edge unless he has the advanced training necessary to handle such a procedure. If the item cannot be taken to the lab, quite often a crime scene technician from your department or another department would handle the preservation of the prints. This technician would have the equipment and special training to do the processing correctly.
If you are involved in the processing, there are a number of considerations to keep in mind:
1. If the item will not corrode, then the item should be allowed to dry at the ambient (surrounding) air temperature.
2. Any item that requires special processing should be turned over to the investigating officer for processing or transportation to the lab.
3. Tests have shown that it is still possible to find identifiable prints up to about five days.
4. Due to their smoothness, glass surfaces and paint-covered surfaces lose print structure much faster than metal surfaces.
5. Keep the item wet until you are ready to process.
6. Superglue fuming and Small Particle Reagent (SPR) application are found to be the most effective methods in recovering prints that have been submerged for any length of time. The photo on the left is a Superglue fuming tool.