A Basic Understanding of Dactyloscopy

            Many do not understand what goes into either the search for latent fingerprints, or the methods of identifications. Perhaps this will help better understand.

            First, what are fingerprints? Look at your hands. Notice how the skin on the palms and fingers (and also the bottom of the feet and the toes) is different from the rest of the body. Our bodies have adapted to the needs of our abilities by forming ridges along these surfaces. These ridges are designed to create friction, to aid in walking and in handling items with our hands. If you continue to look, you will see that these ridges are not symmetrical; they flow into formations, all the while individual ridges abruptly stop, merge into other ridges, or may even be represented as just a dot. These formations and individual details provide the basis for the uniqueness of the prints, permitting their use as an individual form of identification. Along the summits of these ridges are located pores, through which the body exudes waste chemicals both to rid the body of them and to provide for bodily temperature stabilization, the waste commonly referred to as perspiration or sweat. This sweat is made of a number of chemicals, including water, fats, and amino acids. As with all skin, unless severely damaged, it will repair itself, resulting in the permanence of the ridges as an identification tool. From gestation until post mortem decomposition, the ridges will remain intact, unless the dermis is so badly damaged that it results in scarification.

            Fingerprints are deposited in one of three manners. First, one may touch a plastic material, for example putty, and impress the fingerprint onto this material. Second, one may touch a material like paint or blood, and transfer the image of one’s fingerprint to another surface. Finally, the sweat mentioned above spreads along the top of the fingerprint ridges; when we touch another surface, we transfer the image on the fingerprint to that surface as a usually invisible transfer.

            Fingerprints vary among individuals. We each have different skin; various factors result in their being ethno-anthropological differences in skin, so that some groups produce deeper furrows than others. We all have slightly different chemical make-up, and our bodies exude sweat differently, and with different chemical make-up that affects is composition and quantity. For many of us employment has effects on our skin; various trades work with chemicals which have destructive effects on the body and its ability to produce the sweat. Each of these factors will effect the potential for any one of us leaving “latent” fingerprint, composed of sweat, or “patent” (transfer) or “plastic” (impressed) prints.

            Other factors affect the potential of locating prints. An easy one is cleaning. When an area is wiped down, prints are destroyed. Another is environmental conditions. High temperatures and low humidity each work to hurry the evaporation of fingerprint material. Similarly winds will aid in evaporation of the materials. In hot summer sun, especially with a breeze, latents deposited on a surface such as a metal auto body, will very quickly be aged, and their detection hampered if not stymied. Yet in protected areas, a latent may remain for almost indeterminate periods of time, full of life as its oils and other constituent components are not harmed.

            Different surfaces also affect the location of fingerprints. Slick, non-porous surfaces tend to permit easy development of latents, using traditional powder techniques, assuming environmental factors do not harm them. Thin plastic material such as plastic bags requires other techniques to visualize the prints. Porous materials generally require chemical processing – paper products are often processed with ninhydrin, an amino reactive chemical, iodine fumes which react with the fatty components of the sweat, or silver nitrate which reacts with the salts in the sweat. While blood is often thought of as a red liquid, much of it is a clear liquid, and a variety of chemicals are used to visualize fingerprints transferred in it.

            Thus it is far from just dusting a surface to locate a print. Even a beautiful, slick, non-porous surface may host latents that will not adhere to dust. This is where an experienced fingerprint specialist is of value, knowing the variety of techniques and how to use them, to permit searching surfaces that may hide damaged or dried out latents.

            Identification of fingerprints is another misunderstood aspect. Since about 1980, automated fingerprint identification systems have been established that permit “cold” searches of latents. However, currently these systems are only available to the agencies that comprise the criminal justice system; they are generally not available to civil case practitioners due to various privacy laws. Thus in civil work one is limited to comparing against known standards. These may be available from police or regulatory agency files, depending on privacy laws. For clients and cooperating persons inked standards may be obtained. A common misconception is that one may surreptitiously obtain prints from a suspect by having them handle an item and then process it for latent prints. However, this is an especially inefficient method. First, will the suspect deposit all ten fingers on the item? Second, how well with the suspect handle it, how complete will be the latents left behind. What is being done is comparing latent prints to latent prints – and if either is incomplete, or if the “standards” do not include all ten fingers, it is very possible that the finger or area of finger involved will not be obtained to compare against the unknown print.

            Records searches should be conducted against suspects; if either regulatory licensure is found, or a criminal arrest history, attempts should be made to obtain certified copies of the record fingerprints from the record keeper. Perhaps non-public agency fingerprints exist; some employers maintain fingerprints in their records for any of several reasons. Perhaps these may be obtained for comparison. Much like computer work, fingerprint comparison is a garbage in, garbage out proposition – if the “standard” is of low quality, the potential of identifying a latent decreases significantly.

            Associate with a fingerprint specialist; their counsel will help you make the early decisions on how to proceed with an evidence examination much easier in the log run.

Firearms - more than just the barrel of a gun

Most commonly, one thinks of forensic firearms as matching a bullet to the firearm that fired it. But there is so much more that firearms evidence can tell us.

Most people now know that the fired casing can also be matched to the firearm. This is useful when dealing with any incident where casings have been ejected - an automatic, pump action, lever action, or even a revolver or single shot where the firearm was reloaded. The information on a casing is also valuable with unfired ammunition, such as when someone has cycled rounds through the firearm, perhaps from unloading and later reloading it. There are a variety of marks on the case that may be used to tie it to a firearm:

• Breech face marks, which are impressed onto the surface of the case head and primer during the firing of a gun
• firing pin marks, impressed onto the primer when the firing pin impacts it
• extractor marks, which are made by the extractor as it grabs the rim and removes the case from the chamber
• ejector marks, which are applied to the case head during the ejection cycle as the case head impacts the ejector and is knocked clear of the action
• magazine lip marks, from the edges of a magazine sliding across the forward edges of the case as it is inserted and removed from the magazine.

An often overlooked piece of information that can be gleaned from fired bullets is known as General Rifling Characteristics. Manufacturers use the same rifling characteristics as they make hundreds or thousands of any single model of firearm. An examiner, confronted with only a recovered bullet, can measure the widths of the lands and grooves, count the number of them, and determine the direction of rifling twist. Then, the examiner may refer to a collection of data, known as GRC. These collections, once printed and now available in computer formats (indeed, the ATF/FBI NIBIN provides access to such a collection through its database) provides lists of firearms with similar characteristics. Depending on the accuracy of the measurements, the examiner may be able to filter the list down to a very few, or even single, model of firearm. This provides strong investigative leads - I do not need to consider every 9mm Luger pistol if the GRC indicates it could only have originated from a very few models. 

Occasionally, distance may be determined. In a shooting, the victim's shirt is found to have a bullet hole. Lab techniques permit the examiner to test it for the presence of various particulate matter - unburnt powder, burnt powder smoke residue, and primer elements. Using lab techniques, the examiner may visualize a pattern of these particles. Then, using the firearm involved in the case, the criminalist may conduct a series of test shots, over a variety of distances. Here, it is important for the examiner to know and thus use the same type ammunition as was involved before. The test fired target will then be subjected to the same lab tests to permit visualization, and a comparison against the shooting evidence permit an estimation of the distance involved in the shooting. Specific? No. But it does provide a good, generalized distance to be taken into consideration, especially if the question is between close range and moderate range shots. These tests are usually limited to about fifteen feet total range; the particulates do not carry further, and may not carry that far.

Shotgun permit a similar analysis. The combination of shotgun and shotshell load will produce a pattern that will expand over distance. By documenting the evidence pattern first, and then conducting a series of test shots with the evidence shotgun and the same type ammunition, the firearms examiner will be able to establish  the pattern of the shotgun over a variety of distances, and then compare this to the evidence, to come up with an estimated range.

A common practice is to document the trajectories involved in a shooting. Most shootings occur within fifteen meters; at these ranges, ballistic curves do not have great significance. Thus the trajectory can be treated as a straight line. When provided with multiple points, the investigator can track the flight of individual shots, and plot them back to a potential shooting position. This permits the reconstruction of a scene, tracking especially the actions of the shooter.

In a recent case, victims claimed that during a road rage incident another driver had pulled up to their car, fired into the driver's window, the bullet missing the driver and skinning the passenger's forehead. The victims drove home, two counties away. The injured party would not cooperate with the investigation; no documentation was ever made of the wound. Upon returning to the county of jurisdiction, patrol officers did an excellent job of photographing the vehicle and the damage to the driver's window, plus the lack of any of the damage to the vehicle. Two days later the victim driver returned, to show investigators a bullet found in the passenger door map pocket. This was also well documented. A suspect had been developed from their statements; the suspect owned two rifles, which were turned over to investigators, plus showed them an empty box for a revolver, which was stated to have been lost some time previously. The rifles were submitted to a local crime lab; they could not be identified to the bullet. No GRC was conducted. During defense reconstruction, a series of tests were conducted with both rifles and revolvers to determine the behavior of a bullet under the circumstances. In every case, the bullet passed through the first piece of window glass, passed through a witness board representing the forehead, and passed through the second window glass, with no deviation nor apparent loss of energy. The physical evidence would not support the projectile's appearance in the map pocket. Upon examination of the defense's forensic review, the prosecution offered the  defendant a very minimal misdemeanor plea to avoid trial.

When looking at a case, do not overlook the total potential of firearms evidence. It may have much more to tell than is readily apparent. Having your team examine it in detail may bring to light aspects of the case which were previously overlooked.

Maybe and the Identification of Fingerprints

                        In 1979 the International Association for identification (IAI), the primary professional organization among forensic fingerprint specialists, established Resolution 1979 -7. This established that any member or examiner certified under the IAI latent print examiner program, who reported or testified that an identification was "possible, probable or likely" would have committed, as a member, an act unbecoming; if certified, to have action initiated towards certification revocation. In 1980 resolution 1980-5 amended the prior resolution, to further clarify in proper actions in court.

            From its earliest days as a forensic identification medium, fingerprints have been recognized as unique. Only now, with access to computerized automated fingerprint recognition systems, can truly in-depth research we performed. However, the experience of researchers and practitioners, augmented by statistical modeling, has served to form strong underpinnings for this theory.

            The past 20 years have seen challenges to the standing of fingerprints within human identification. Several critics of fingerprints, themselves neither experienced examiners or scientists, have attempted to belittle fingerprint technology rhetorically. If anything, their efforts have strengthened the primacy of dactyl identification by spurring greater research into fingerprints from biological, mathematical, and file compare to efforts.

            A second threat has been due to the human factor. First, there have been several episodes of malevolent, fraudulent fingerprint identifications by examiners lacking ethical and moral strength. Second, there have been a number of incorrect identifications reported by examiners. In the worst American case, three FBI examiners agreed, incorrectly, to the identification of a latent fingerprint from an international terrorist case -- when the originating nation’s police had already correctly effected an identification of a known terrorist. To its credit, the fingerprint community responded by upgrading policies and procedures, to the extent of some agencies requiring blind review of all latent figure print work by a separate examiner. Further, it has keyed psychological research to better understand how an examiner establishes a conclusion, as well as to understand how independent examiners can come to the same, incorrect, conclusion.

            Since the early days of latent fingerprint identification, it has been a tenet of the field that conclusions are firmly, positively established. Many misconstrue this as the examiner's being set up as demi-gods -- infallible. What it has really meant is that an examiner would not report a conclusion except:

·       the latent was produced by this individual

·       the latent was not produced by this individual

·       the latent use of insufficient quality to render an opinion on sourcing.

Resolutions 1979 -7 and 1980 -5 were enacted to provide the IAI a degree of authority to sanction those who violated these principles.

            In July, 2010, the IAI adopted Resolution 2010 -18. This resolution rescinded the prior resolutions, and effectively scrapped the authority of the IAI to sanction a member or certified examiner who should report a latent as being potentially produced by an individual. Specifically, section 7 speaks of using mathematical models to support possible identifications, and section 8 requires the examiner provide additional factors than merely mathematical modeling to support the qualified conclusion.

What this foretells is tremendous confusion in the justice arena. Investigators, long accustomed to knowing a positive conclusion to be considered a firm fact, will now have to determine how much weight to give it in making case decisions. More likely, many investigators will continue as in the past, and act upon a qualified identification as if it were firmly based. Prosecutors will face similar challenges. Defense, which previously could examine the quality of the examiner’s work product, or possibly challenge what an identification meant (“yes it is the defendants, but he has legitimate access”), now will face having to mount significant technical evaluation of the latent comparison, and possibly end up with a battle of the examiners when the qualified examination of one specialist cannot be verified by another.

            A significant fear will be that of the relatively inexperienced examiner determining a "maybe." Unless agencies act to establish in-house protocols limiting such determinations, or requiring verification of the qualified results, the determinations of and inexperienced examiner will be entered into the record as the equal to those of highly experienced examiners.

            Especially for defense counsel, the use of an experienced, senior, fingerprint specialist will become mandatory. To help maintain quality in the criminal justice system, not just for high profile, major felonies, but indeed for any case where fingerprint evidence has meaning. The costs to the justice system will expand significantly.

            The implications of this policy change by the IAI will be significant, to say the least. As a firm believer in fingerprint identification as a valuable form of evidence, I fear the unintended consequences it may unleash.