Fingerprints What TheyCan & Cannot Do! (The following paper was the text of a presentation at a training seminar for Los Angeles County Deputy District Attorneys on November 14, 1992) By ALAN L. MCROBERTS Los Angeles Sheriff's Department Scientific Services Bureau --— Identification Section The science of fingerprints is an applied science. Its foundation of uniqueness and permanence is well established in the sciences of anatomy, embryology, and genetics. When we also include the sciences supporting fingerprint development or enhancement techniques, we would add chemistry, physics, photography, and computer sciences. The identification process is an application of scientific comparison methodology. Present on the inner surface of the fingers and hands (palmar) and the bottom surface of the feet (plantar) is skin which is corrugated or rough. This “volar” skin consists of raised portions which are known as ridges. These “papillary” ridges do not run from one side of the hand or the finger to the other in a continuous stream, but are broken and noncontinuous. The arrangement of these ridges, like all natural things, is unique. The raised ridges increase the frictional qualities of these surfaces, aiding in the ability to grasp items, thus the term “friction skin”. Present on the top of the friction skin, or papillary ridges are minute sweat pores which exude perspiration. This perspiration, as well as other contaminants, may adhere to the surface of these ridges. When an object is touched and the residue is transferred or deposited, a recording of these ridges may be left on the item. The word “latent” by definition means invisible. This type of print needs some kind of powder, chemical, or electronic processing, or enhancement, to make the latent print visible. However, “the term latent print is commonly applied to all chance or unintentional impressions of evidentiary values”1, whether visible or hidden. The concept that “something may adhere and may be transferred is important”. Often, detectives are disappointed and prosecutors are frustrated with the lack of the irrefutable evidence of the suspect's fingerprints on a particular item of evidence, which he must have handled. It is unfortunate that, unlike on television, the “suspects” prints don't always appear. A look at the factors influencing the chances of obtaining prints will assist in understanding the fragile and elusive nature of latent impressions. Each of the following various factors independently or in combination can account for the lack of prints on a surface: 1) Individuals don't always have a sufficient quantity of perspiration and/or contaminates on their hands to be deposited, 2) When someone touches something, they may handle it in a manner which causes the prints to smear, 3) The surface may not be suitable for retaining the minute traces of moisture in a form representative of the ridge detail, and 4) The environment may cause the latent print to deteriorate. The most important fact dealing with the lack of fingerprints is that it neither suggests, implies, or establishes that any person did or did not touch the item of evidence. Items which have been witnessed to have been handled and laboratory experimentation repeatedly reiterate this premise. (I have used the following example and explanation in court many times. If I were to provide a clean, smooth piece of glass to the jury and have them hand it from one to another and then I were to process it for fingerprints, I would not have the expectation of obtaining identifiable prints for each juror on that glass. Although the surface of the glass is what most technicians would agree is a superb surface for obtaining prints, not all of the donors would have perspiration and/or contaminates on their hands, (some individuals have very little natural palmar perspiration), some would probably grasp with such firmness they would smudge or smear their prints, and some would touch the surface in the same location as a previous donor's print). When a report reads “no prints”, what does that really mean? It means no prints of evidentiary value were preserved. It does not mean that the item was wiped down, or that no one had ever touched or handled it. Occasionally observations to establish that the item has been wiped down may be made and reported, but it usually would not be possible to determine at what point it was wiped or even if the item had been handled since the wiping. The term “no prints” does not mean that there were no marks or smears--—it means that if any markings were present, they lacked sufficient detail to be of evidentiary value. As there are limits to the collection of prints at all scenes, an evaluation of what should be preserved as evidence is a necessity. Technicians cannot develop, preserve, document, and collect all fragmentary portions of ridge detail at crime scenes. Realistic expectations and a point of diminishing return are factors with which to reckon. The evaluation of latent prints for retention is one of the most difficult areas to define. As all latents vary in degree of clarity and amount of visual information, all latents need to be evaluated on an individual basis. Any latent print which is identifiable would obviously be of value. And, a latent print or lift lacking any detail (smudge) would clearly be of no value for identification purposes. Prints of no value need not be retained; as the name “no value” implies, there is no evidential value. However, the act of not retaining an item of potential evidence requires a thorough understanding of the term “no value”. Unidentifiable prints from a location indicating involvement in a crime (i.e. prints on a point of entry which suggest the forced opening of the window) may have value in the eyes of the defense attorney, in spite of the prints lack of being identifiable. Defense attorneys may rightfully argue that a comparison of those non--identifiable prints could possibly exclude their clients from being the donor. The level of visual information in a latent print needed for making an elimination is different than what is necessary to make an identification. Although Olsen is speaking of identifiable prints in the statement “latent prints found at a crime scene and which are in such a position or location that only the perpetrator of the crime could have made them, assist immeasurably in eliminating all other suspects”2, this premise is still valid even when applied to non--identifiable latents. All unidentifiable prints in such a position or location, if they could assist in the elimination of a suspect, must be retained. What frequently is offered by defense counsel is the inaccurate generalization of any print being useful to eliminate the defendant. This defense by elimination can only be legitimately applied in cases where “only the perpetrator of the crime could have made them”3 (the prints). In the case of the prints on the window, was there a second suspect to whom the prints could have belong--—in which case, the elimination defense is now invalid. The age of or the dating of a print is often desirous and, if possible, could determine factors significant to most judicial proceedings where latent prints have been obtained. Unfortunately, very few situations arise where it is scientifically possible to accomplish this task. One principle reason for this is the unknown constituents of the latent print itself. Without this knowledge (not assumption) no amount of speculation or even experimentation could be considered definitive. There are just too many variables. The novice and, unfortunately, sometimes even the experienced technician (who lacks thorough training and study) will suggest or refer to it as a “fresh” print because the latent readily absorbed the powder and caused the print to develop quickly. Cowger states, “a latent print [which] develops strongly and quickly does not provide much of a clue to its age since many substances that could cause the print may have sufficient viscosity to remain in one place for long periods of time and do not necessarily dry out even in harsh environments”4. The burden is on the detective to establish a limited time frame of access through witnesses. Witnesses must prove either 1) the suspect never had legitimate access or 2) the surface where the print was located was thoroughly cleaned after the suspect's most recent lawful access. The technician may occasionally provide some help. For example, having observed that a thin layer of dust was present on the surface--—to the exclusion of the areas where the prints were developed--—would establish a time frame more recent than the last cleaning of that surface. Occasionally, an experienced examiner may offer or be solicited by counsel to offer selective testimony such as; A latent print of only natural palmar perspiration (mostly water) would not be able to survive for an extended period of time while being subjected to harsh environmental conditions. This statement itself is accurate. However, if the statement is not qualified with the fact that unknown constituents deposited with the print may alter the expectation of print survival, the testimony of the examiner would not provide the whole truth, and the objectiveness of the witness could be seriously questioned. If the circumstances and observations of a particular case would permit testimony regarding the age of a print, it would still require, as Cowger suggests, that the testimony “be a subjective evaluation of what is objectively considered, even then it must be offered only as an estimation based upon the examiner's experience and not excluding other interpretations.” It is commonly explained that “Fingerprints are compared by examining the ridge characteristics of two different impressions to determine if they occupy the same relevant position and area. Identifications are effected by viewing these ridge characteristics, taking into consideration the similarity of the characteristics, the number of characteristics, and the unit relationship of the characteristics to each other.”5 This description of the comparison process is accurate, but prosecutors often desire an even more detailed explanation of the methodology. My explanation would provide an outline of the process as three stages during the course of an examination --— Analysis, Comparison and Evaluation.6 During the analysis phase, the area of friction skin suspected of making the print is determined and the clarity and variety of details present are established. The comparison phase consists of observing the details established during the analysis of the unknown print and comparing them to the known exemplar. The comparison begins at a common location in the unknown and known prints. It then extends to include additional details of the ridge formations. During the comparison phase, evaluations may also be taking place. These evaluations are to determine sufficient uniqueness. An identification is established after the comparison phase has shown the friction ridge formations within both prints to be in agreement and the unknown print has been evaluated and determined to have sufficient uniqueness to establish individuality. Each case must be individually evaluated for sufficient uniqueness. Sufficient uniqueness is a subjective determination by the examiner based on the individual's training, experience, and abilities as his skills are applied in the evaluation of any particular print. The evaluation will be influenced by the clarity of the print, the rarity of the overall appearance or pattern, the quantity of ridges, the number of ridges between the characteristics or minutiae, the types of characteristics, the relative positioning of characteristics, and can even include the shape of the ridges and arrangement of the pores along those ridges (if the clarity allows for examination of pore placement). A final aspect of our scientific comparison methodology is the standard within the field to require a verification on all latent print identifications. It should be distinguished that “the verification is not part of the identification process. It is a very important part of the scientific process.”7 As prosecutors, if you have occasion to have a witness willing to testify to a latent identification without the verification, beware of this breach of protocol. In the description of the methodology, it was stated that the identification is established after the comparison has shown the friction ridge formations within both prints to be in agreement (from a common source) and the unknown print has been evaluated and determined to have sufficient uniqueness to establish individuality. What is “sufficient uniqueness”? This is one of the most frequently asked and inadequately answered questions. It is commonly phrased “How many points do you need for an identification?” To repeat what is hoped you have heard time and again “there is no valid scientific basis for requiring a minimum number of ridge characteristics which must be present in two fingerprints in order to establish positive identification.”8 Examiners will occasionally avoid an in--depth answer by replying “I'm comfortable with...”. A Federal Court Judge recently charged “If you only [have] 10 points, you're comfortable with 8; if you have 12, you're comfortable with 10; if you have 50, you're comfortable with 20.”9 Based on that court's experience of inconsistent levels of “comfort” he denied the admission of the evidence. Examiners are providing counter--productive testimony when testifying to some arbitrary number they have selected. The fact of the matter is “there is no valid scientific basis for requiring a minimum number”. The Federal Bureau of Investigation is often mis--quoted as requiring twelve. This is inaccurate as they have no set minimum. The book, “The Science of Fingerprints”, refers to charted enlargements stating that “twelve characteristics are ample to illustrate an identification, but it is neither claimed nor implied that this number is required.”10 The scientific comparison process cannot be reduced to a simple counting of ridge characteristics. Even the question--—How many characteristics did you find matching in both prints?--—leads to this undermining and oversimplification of the comparison process. Historically, many explanations of the comparison process frequently suggest the print in question must not have any unexplainable dissimilarities. On numerous occasions, this premise has provided the defense with a point of confusion in terminology, which has caused disastrous results. By definition, dissimilarity means not being the same --— it's different. Dissimilarities can only occur in prints that are of an uncommon source. “That is why during a Latent Print Examiner's early training they are taught if a print has a dissimilarity, you do not have an identification.”11 Distortion, however, is defined as changing the usual or normal shape, form, or appearance. All prints have various levels of distortion. The defense attempts to use these terms interchangeably as a method of attack on many identifications. Due to confusion about these terms, experienced latent print examiners have been known to mistakenly testify to the phrase, “no unexplainable dissimilarities” as a requisite for an identification. They then go on to allow for the possibility that if a dissimilarity were found, it would invalidate the identification. If a legitimate identification has been made, there is no possibility that a dissimilarity exists. These witnesses must be rehabilitated or the defense can provide another “expert” who will direct the attention of the jury to some distorted detail and refer to it as a “dissimilarity.” The defense attorney would then offer the identification as invalid using the definition offered by the prosecution's own witness. Admittedly, there is confusion within the field on the use of these terms; however that issue is being addressed. Earlier it was discussed that along the top of the friction skin ridges are minute sweat pores which exude perspiration. And that this perspiration, as well as other contaminants, may adhere to the surface of these ridges and be transferred to surfaces, leaving latent prints. And that these latent prints need some type of powder, chemical, or electronic processing to make the latent print visible. What are these processes that are utilized to develop or enhance the latent print? The minute quantities of perspiration and/or contaminant transferred or deposited is typically unknown to the technician processing the evidence for latent prints. Without a knowledge of the constituents of the latent print, processing techniques must be applied in a sequence suitable for the majority of cases. Various factors influence the selection, or sequential processing. Some of those factors are: surface type (porous or non--porous), conditions of the surface (i.e. dirty, greasy, oily), constituents of the latent print (when known), any known environmental conditions to which the evidence has been subjected (has the item been wet), personal preference, processes available, and the type of case and workload (or how much time and effort can be expended). Most of the fingerprint references expound the various techniques useful to develop latent prints. The variety and variations of techniques is as vast as the number of surfaces which may be processed. No single reference can be considered as complete or exhaustive. New techniques and variations of existing methods are continuously discovered or refined. Take, for example, a non--porous surface such as a ziplock baggie. Fifteen years ago, the item would probably have been processed with either black, silver, or magnetic fingerprint powder, depending on the technician's preference and departmental supply. Approximately ten years ago, it may have been treated with cyanoacrylate (CA) or superglue fumes and then photographed if the print were visible, or further processed with a choice of powders. Five years ago, it may have been CA fumed, powdered, and dye stained with Rhodamine 6G dye that could penetrate the very faint CA developed print and would fluoresce when examined under a laser. Today, we can add two additional dye staining solutions in sequence for use with other forensic light sources that provide a variety of wavelengths or colors of light. However, the basic application of powder processing is still a valid technique and when prints have been developed in this manner, their significance should not be lessened because they were not developed with a more sophisticated method. The subject of processing techniques has become very complex. It takes personnel actively working in the research area to stay current with the most recent developments. The implementation of all the available procedures is not realistic for most agencies. Some procedures such as Vacuum Metal Deposition require investments of over a hundred thousand dollars for the initial equipment. Processing techniques for the development of fingerprints are unlike procedures used in the various forensic science disciplines, where results may depend upon the procedure involved or false conclusions may be drawn from the testing. “Techniques for developing or enhancing latent prints do not add ridge characteristics which are not present originally. At worst, an improperly used technique would hinder or prevent the identification of a latent print by obscuring or destroying ridge details. Such an occurrence is to the benefit of a suspect rather than his detriment.”12 When an examiner is attacked for his choice of techniques, it is an effort to cloud the issues and lessen the value of the print. The importance of the success of the technique utilized should be stressed. There are several negatives about fingerprints--—not being able to determine the age of a print, not always developing a print even though an object was obviously touched, the lack of a definitive quantitative measure necessary for an identification, wide variations in processing techniques, and even, a lack of consistent terminology within the field. Some of these factors may see change in the years to come, but none of them should ever be allowed to diminish the value of a fingerprint identification. ENDNOTES 1. Olsen, R.D., Sr., Scott's Fingerprint Mechanics, C.C. Thomas, Springfield, 1978, p 114. 2. Ibid p 113. 3. Ibid p 113. 4. Cowger, J.E., Friction Ridge Skin, Elseview, New York, 1983, P 108. 5. Hazen, R.J. and Phillips, C.E., The Expert Fingerprint Witneess, U.S. Government Printing Office, 1981, pg 15. 6. Ashbaugh, D.R., Ridgeology--—Modern Evaluative Friction Ridge Identification, published by Royal Canadian Mounted Police, no date, pg 28. 7. Ibid p 30. 8. Olson, R.D.Sr., Scott's Fingerprint Mechanics, Thomas, Springfield, 1978, p 27. 9. Trial transcript, Peo. v. Kenneth Theodrick Parks, Los Angeles District Federal Courtn, No. CR 91--358--JSL, vol. 5 p 1. 10. The Science of Fingerprints--—Classification and Uses, U.S. Government Printing Office, 1984, pp 194--195. 11. Leo, W.F., Dissimiliarities and Distortion in Friction Skin Identification, pre--published copy, pg 1. 12. Olsen, R.D., Sr., Scott's Fingerprint Mechanics, Thomas, Springfield, 1978, pg 436. This article was originally published in “THE PRINT” Volume 10(7), June 1994, pp 1-3 and has been obtained from the online library provided by the Southern California Association of Fingerprint Officers www.scafo.org