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Crime Scene Processing Evidence Processing Iowa Death Investigator's Association Crime Lab Reports for All Non DPS Agencies |
IOWA DIVISION OF CRIMINAL INVESTIGATION
Examiners at the Iowa Division of Criminal Investigation Laboratory are called Criminalists. Criminalists in the Impression Evidence Section of the Laboratory undergo over 3,000 hours of in-house training with a senior latent print examiner. These studies include the history and theory of fingerprint and footwear/tire track identification; physiology of friction ridge skin; footwear and tire manufacturing techniques; latent print processing techniques; legal issues; expert witness testimony; and report writing. Along with this extensive training at the laboratory, they will attend outside training sponsored by the Federal Bureau of Investigation, The International Association for Identification, Midwest Association of Forensic Scientists, and other professional organizations. After successful completion of the training program the Criminalist trainee will complete a six-month apprenticeship under the direct supervision of a senior examiner. Upon completion of the apprenticeship, the Criminalist will be able to perform examinations of evidence submitted to the DCI Laboratory. Services Offered by the Impression Evidence Section Criminalists in the Impression Evidence Section at the Iowa Division of Criminal Investigation Laboratory examine submitted evidence for the presence of friction ridge skin impressions; shoe and tire impressions; and make physical matches. They develop, preserve and collect these impressions. After discovery of unknown impression evidence, they compare the unknown impression to submitted known examples. Upon completing the comparison, the examiner renders their scientific conclusion and writes a report of the results of their examination. Often they are called upon to testify in courts of law as to the results of their examination. These services are provided to the Law Enforcement community of Iowa at no charge. What is friction ridge skin? Friction ridge skin is more commonly known as fingerprints. Friction ridge skin is the skin that in on the palms and fingers of the hand and soles and toes of the feet. Friction ridge skin has raised ridges and furrows between them; this corrugated surface is designed for grasping and holding items. At the tops of the ridges there are sweat pores. The ridges do not simply start on one side of the finger and travel straight and uninterruptedly to the other side of the finger but rather these ridges stop, start, and branch into multiple ridges to form unique and individual patterns. Friction ridge skin forms in the 12th to 16th week of fetal development, and except for changing in size due to growth, remains the same throughout a persons life until decomposition. What is a latent print? A latent print is a chance or accidental reproduction of some area of friction ridge skin; by definition, "latent" means hidden or not visible. The pores at the tops of the friction ridges are constantly exuding water and waste products, which cover the friction ridges. When items are touched, this moisture, along with any other contaminates are deposited on the surface of the item in the pattern of the friction ridges, not unlike a rubber stamp. Since the latent print is not visible some development process must be used to make the latent print visible. What is a known print? A known print is a deliberate reproduction of some area of friction ridge skin. This is most often done by applying printers ink to the fingers or palm and placing them on a white fingerprint card, producing a reproduction of the friction ridge pattern. Why are fingerprints used for identification? The two principals used for fingerprints as a positives means of identification are that fingerprints are permanent and unique. This means that an area of friction skin of an individual will not be duplicated on their own hands or feet nor on any other persons hands or feet. How are fingerprints compared and identification made? The stopping, starting and branching in to multiple ridges occur randomly. These form the individual ridge characteristics that examiners look for. An examiner will do a side-by-side comparison of the unknown, or developed latent print against the known print. This is usually done by using a five-power magnifier. The examiner looks for the same type of individual ridge characteristic, in the same location, in both the unknown and known prints. These individual ridge characteristics must be in the same unit relationship to each other, for instance if there are two ridges between two ridge characteristics in the unknown print, there must be two ridges between the same two ridge characteristics in the known print. If there is a sufficient quantity of those individual characteristics found with no unexplainable differences, then the examiner can state that the same person made the developed latent print and the known print. This is to the exclusion of all other persons. How long will fingerprints last? There is no scientific way to know how long a latent fingerprint will last. Fingerprints have been developed on surfaces that had not been touched in over forty years; yet not developed on a surface that was handled very recently. There are a multitude of factors that effect how long fingerprints last. Some include the type of surface touched; the individual who touched it, and environmental conditions can have serious bearing on how long a fingerprint will last on a surface. Can you tell how old a fingerprint is? There is no scientific way to date the age of a developed latent fingerprint. The only possible way to know the approximate age of a latent fingerprint is to know the last time that the surface that the developed latent print is on was thoroughly cleaned. Generally latent print residue will not survive a thorough cleaning, so if a latent print is developed it was probably deposited after the cleaning. Do identical twins have the same fingerprints? No, no one has the same fingerprints; although identical twins have the same DNA, they have different fingerprints. What can fingerprints be recovered from? Under the right conditions latent prints can be recovered from almost any surface. As technology advances the opportunities to recover latent prints has also advanced; so that now surfaces that would not have been checked for latent prints years ago routinely yield latent prints. How are footwear and tire track impressions examined? Almost exactly as fingerprints are compared, life size reproductions of the unknown impression whether in a photograph or cast of the original impression are compared to the shoe or tire. The examiner, to assist in the comparison, sometimes also produces inked known impressions of the shoes or tires. How are footwear and tire track impressions identified? Most shoes and tires have tread designs on the bottom of them. This design is placed on the shoe or tire by the manufacture. The function of the design is not unlike the function of friction ridge skin it is for traction or gripping. All of the shoes and tires of the same type are manufactured with the same design. Each individual piece of the design is referred to as an element. When the shoe or tire is used subtle changes occur to them caused by contact with the ground or other types of damage or injury. This damage from the use or abuse of the shoe or tire is specific to that individual shoe or tire. Although all the shoes and tires of the same type start out looking alike, through wear or damage, this changes. What conclusions can be made from footwear and tire track impressions? Unlike fingerprints where the conclusions are either the print was made by or not made by a specific individual, footwear and tire track examinations have a range of conclusions. Footwear and tire tracks can be identified as having been made by a specific shoe or tire. In other words that shoe or tire made the unknown impression to the exclusion of all others. A shoe or tire can be absolutely eliminated as having made an unknown impression. If the designs in the unknown impression and the known shoe or tire are different; or it has the same design but the elemental size is different, it is easily concluded that the specific shoe or tire did not make the impressions. The conclusion on being made by a specific shoe or tire occurs when enough individual characteristics (damage) are visible on the unknown and the same characteristics appear on the known shoe or tire. If the unknown impression has an insufficient amount of individual characteristics, for an identification, but does have some individual characteristics in common the examiner may say that it is highly probable that a specific shoe or tire made that impression. In the event that the impression has the same design and size but no individual characteristics are visible, the examiner would conclude that the impression and the shoe or tire are consistent in outsole or tread design. This means that they the known shoe or tire could have made the impression, but so could have all the shoes or tires of that design and size. What is meant by outsole? An outsole is the portion of a shoe that contacts the ground, i.e. the bottom of the shoe. The outsole is where the tread design appears. Can you tell what size a shoe is from an impression? Not in most cases as most impressions are just partial impression and dont have the entire shoe dimensions. Different styles of the same size shoe may have different sizes of outsoles. An example, Brand As "Zippy" style, size 7 shoe may have a 8 inch outsole, while Brand As "Zort" style, size 7 shoe may have a 71/2 inch outsole. Brand A and Brand B may have different size shoes of the same length. Some styles of shoes have the shoe size printed on the outsole, if that is the case and that part of the shoe in reproduced in the unknown impression then size determination is quite easy. Can you tell the brand from the impression? In some cases it is possible to tell the brand of a shoe or tire from the unknowns impression. There are reference materials that allow searches of specific tread designs in both shoes and tires. Also distinctive logos, particularly on shoes causes easy brand identification. It should also be noted two or more companies might produce shoes or tires having the same tread design. Why is brand determination important? Brand determination can be a valuable tool for the investigating officer, knowing what brand of shoe or tire impression was left at the scene of a crime can assists the officers in their investigating. For instance if a Nike brand shoe impression is found at the crime scene and an empty Nike shoe box is found at the home of the suspect, this could be important information. For more information please visit the following web sites: |
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| Created: 02-07-2006 Last Updated: 11-17-2009 (JLR) |
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