PRESERVING LATENT PRINTS:
Latent prints on nonporous evidence are often deposited on the surface of an item and are extremely fragile. Wearing gloves does not protect the latent prints from being destroyed if they are touched, rubbed, or smeared; they only prevent additional prints from being deposited.
Life of latent prints:
Unless there is a witness to the offender handling a piece of evidence, there is no way of knowing when the item was touched by him/her. It could be days, months, or years since something was handled by the offender.
Factors Effecting the deposition of latent prints on an item:
Air, temperature, and water all have an effect on the survivability of latent prints, and their successful development. Moderate air currents will cause gradual evaporation of the water portion of perspiration, while stronger winds will cause rapid evaporation, having little immediate affect on the remaining salts, amino acids, fats and lipids. Air temperature and the temperature of the surface the latent print was deposited on can also have an effect on the latent impression. If the surface is hot, it may cause rapid evaporation. A cold surface can eventually create condensation, as in the case of a glass of cold water on a warm day. Generally, an individual perspires less during low temperatures. High humidity can cause moisture to condense on an object's surface, possibly causing the latent deposits to be distorted or to wash away. Low humidity will cause rapid evaporation of the water portion of perspiration because of the lack of moisture in the air. Rain may wash away a non--fatty/oily latent print deposited on an object's surface. Dew and snow, much like rain, will adversely affect the latent print. Not only will they combine with the water in perspiration to dilute the latent print residue, but they may form a barrier between the surface and the friction ridge skin. This barrier may prevent residue from being left in sufficient quantity to be detected.
What happens to the evidence between the times a latent print is deposited and the time it is recovered can greatly affect the processing outcome. Damage to the can be permanent or temporary, depending on the circumstances.
Considering perspiration alone, the amount transferred from the skin to the object touched is the main factor bearing on the identifiably of latent prints. Perspiration excreted from the fingers and palms is reported to contain from 98.5 to 99.5 per cent water, and 0.5 to 1.5 per cent solid matter. There may be insufficient perspiration to which developing agents can adhere, either because there was little initial perspiration on the skin or because one or more objects were handled prior to the evidence being handled. When sufficient perspiration accumulates on the skin, it should yield a clear impression to which developing reagents will adhere. The anxiousness or nervousness of the individual may also have an effect on the secretion of perspiration through the pores.
Evidence can be difficult to process due to various reasons such as the condition of the surface and the limited smooth area available for processing. Fingerprints can also become superimposed or smudged because of the way an item of evidence is handled, or because the surface is dirty, oily, or greasy. While many investigators wear gloves when handling evidence, there is always the risk that they may become careless and destroy prints.
Latent Print evidence can typically be divided into two categories: Porous and Non-porous:
Porous evidence such as paper, unfinished wood, cardboard, etc., is normally conducive to the preservation of prints because latent print residue can soak into the surface.
Non-porous evidence such as plastic, glass, metal, foil, etc., is much more fragile because the latent print residue may just be lying on the surface. Even the slightest handling can "wipe away" a latent print on non-porous surfaces.
Preservation of Fingerprint Evidence for Collection or Preservation:
The primary concern in all cases is not to add anyone else’s fingerprints to the evidence, or destroy the ones that may be present. Handle all evidence with great care keeping in mind that you could easily destroy prints with careless handling. Most fingerprints submitted will be on paper, glass, metal, or other non-porous objects. When articles containing latents must be picked up, touch as little as possible, and then only in areas least likely to contain identifiable latents, such as rough surfaces. While gloves or handkerchiefs may be used to pick up such exhibits, any unnecessary contact should be avoided. Although using a cloth to pick up exhibits prevents leaving additional prints on the articles, the cloth will frequently wipe off or smear any prints originally present, unless great care is taken. Large articles such as glass, metal articles, and firearms containing latents should be placed on wood or heavy cardboard and fastened down with a zip tie to prevent shifting or contact with the side of the box they are package in if contact is made it could obliterate the latents. Papers and documents containing latent prints should be placed individually in a manila envelope. Do not fold papers once opened. Do not open and pass around letters you want latents prints lifted from. If you do so it will be necessary to fingerprint each person that had handled the paper.
There is zero tolerance for friction ridge identification error in forensic science.
Latent Print Identification and Verification:
When using the scientific procedure of ACE-Vthe steps are as follows:
Analysis – the qualitative and quantitative assessment of Level 1, 2 and 3 details to determine their proportion, interrelationship and value to individualize.
Comparison – to examine the attributes observed during analysis in order to determine agreement or discrepancies between two friction ridge impressions.
Evaluation– the cyclical procedure of comparison between two friction ridge impressions to effect a decision, i.e., made by the same friction skin, not made by the same friction skin, or insufficient detail to form a conclusive decision.
Verification – an independent analysis, comparison and evaluation by a second qualified examiner of the friction ridge impressions.
LEVEL 1 DETAIL:
Friction ridge flow and general morphological information
LEVEL 2 DETAIL:
Individual friction ridge paths and friction ridge events, e.g., bifurcations, ending ridges, dots.
LEVEL 3 DETAIL:
Friction ridge dimensional attributes, e.g., width, edge shapes, and pores
WHAT ARE LATENTS PRINTS MADE OF?
The latent fingerprint, deposited on a surface, is a complex mixture of natural secretions and contaminates from the environment. Three types of glands are responsible for the natural secretions of the skin, the sudoriferous eccrine and apocrine glands, and the sebaceous glands. The sudoriferous glands are distributed all over the body and produce the sweat. Eccrine sweat is approximately 98.5 per cent water, the remainder being principally made up of mineral salts, eg, sodium chloride, organic acids, urea and sugars.
The major chemical constituents of the glandular secretions CONSTITUENTS SOURCE INORGANIC ORGANIC eccrine glands chlorides metal ions sulfates phosphates ammonia water (>98%) amino acids urea uric acid lactic acid sugars creatinine choline apocrine glands iron water proteins carbohydrates sterols sebaceous glands fatty acids glycerides hydrocarbons alcohols
ADDITIONAL LATENT PRINT EVIDENCE INFORMATION:
In criminal cases, if latent prints are recovered from evidence, it’s a relatively simple matter to obtain the inked fingerprints of an individual to compare to the latent prints. If the individual has fingerprints on file from a past arrest or various non-criminal purposes (i.e. military or security checks), they are available to law enforcement agencies. However, in civil cases, obtaining fingerprints of a subject for comparisons can be difficult. In suits pending before a civil court, attorneys may attempt to have the court require an individual to be fingerprinted for comparison purposes, or the court may require an agency with the subject’s fingerprints on file to provide a copy of the prints. One method of obtaining fingerprints of a person for comparison to latent prints is to covertly obtain them. This is normally accomplished by arranging for the person to handle paper items (envelopes, letters, or other documents), drinking cups (paper, Styrofoam, plastic, or ceramic), or other clean porous and non-porous items that have not been touched by too many other people. These can be processed for latents with the hope that any latent prints developed belong to the person in question. This is not a reliable method of obtaining the prints of a person, nor a positive form of identification even if a comparison matches one of the prints with one of the latents for the following reasons: It’s unknown if the covertly developed latents actually belong to the person touching the item because the person’s print was not taken in a controlled situation with each finger being recorded and labeled. Other people’s prints may be on the item touched by the subject, mainly on porous items where prints can last for years. Everyone has ten fingerprints; but when touching an item, they may leave only one or more of these prints.
Example: A person’s left middle and left ring finger could be developed as latent prints on a piece of evidence, but their right thumb and left index finger may be developed on the covertly obtained object. Sometimes a print is deposited on an item when a person touches it. The person may touch the same item later and not leave a print.
To avoid contamination of evidence that may contain DNA, always take the following precautions:
Wear gloves. Change them often. Use disposable instruments or clean them thoroughly before and after handling each sample. Avoid touching the area where you believe DNA may exist.
Avoid talking, sneezing, and coughing over evidence. Avoid touching your face, nose, and mouth when collecting and packaging evidence.
Air-dry evidence thoroughly before packaging. Put evidence into new paper bags or envelopes, not into plastic bags. Do not use staples.
Seminal Stain Collection:
Seminal stains are often, but not always, found on clothing, blankets, and sheets. Allow any stains to air dry, wrap in paper, and package evidence in paper bags. Never use plastic bags to store the sample. Bacteria will attack the sample and cause it to mold making it useless. Label all garments such as under shorts, panties, or other exhibits and package each garment separately in a clean paper bag. If damp, allow fabric to dry completely before packaging. Handle fabrics as little as possible.
Always wear latex gloves when handling possible DNA evidence. Change gloves after each piece of evidence is picked up and packaged. Reglove and pick up the next piece.
Each person sheds approximately 40,000 skin cells an hours or about 960,000 a day
Identical twins have the same DNA profile (however in the future research may detect small variations)
Mitrochondrial or MtDNA is sometimes called maternal DNA is inherited from your mother. It is present in hair, nails, bone and teeth.
Nuclear DNA is contained in all cells in your body and is the same in each cell. Nuclear DNA contains genetic material from both parents.