Fingerprint age determination is not a new concept. Many have realized the benefit that an accurate method of dating a latent print would provide. Convictions can hinge on whether a particular print was left during the commission of the crime or might have been left at a prior time, as is usually claimed by a defendant. For this reason and others, numerous attempts have been made to establish an accurate test for latent fingerprint age determination.
First, a distinction should be made between age determination and “time of placement”. If the suspect was seen handling an item, and it could be proved that he had not had access to the item before or after that time, then it could be said with certainty that the latent print could only have been left at that time. For example, if the newspaper bearing the latent print in question was dated the day before the crime, the suspect’s statement that he was in the victim’s home several days prior to the crime, and not after, could be refuted. Another nonexperimental method to establish the time of placement of a latent print would involve items that are regularly cleaned or washed. It can generally be said that a latent print residing on such a surface was left more recently than the last thorough cleaning. These, and other similar situations, demonstrate how nonexperimental methods can sometimes establish the “time of placement” of latent prints. However, the scope of this article will consider only age determination from an analysis of the latent print residue itself.
Some have claimed that the appearance of a latent print upon development with powder can offer insight as to the age of the print. An examiner may infer that a latent print is “fresh” based on how the powder adheres to the ridges, or on the clarity of the ridge detail. In State v Hulbert (1981), a fingerprint technician testified that latent prints developed on window glass from a home burglary were made “within the previous two days” [l]. He drew his conclusion from the fact that the fingerprint powder “went on fast”. When the Frye [2] test is applied, this method of age determination fails; it has not been generally accepted in the field of fingerprints. Further, under Federal Rule 702 [3] and recent Daubert criteria [4], this method would most likely be considered unreliable. Many factors could cause some older prints to absorb powder just as “fast”. A 1975 study of the effects of temperature and humidity on latent print deposits concluded that “the clarity of a developed print is primarily related to the original latent print quality” and that “it is not possible to determine that a fingerprint is fresh or several weeks old by...observing how the print develops when the dusting powder is applied” [5].
Experiments to calculate the approximate age of a latent based on estimated environmental conditions have been used on many occasions. One of the most extensive examples of this approach can be found in Poland, where the Dactyloscopy Department at Civic Militia Headquarters has created a database that they use to calculate the age of fingerprint “traces” [6]. The database uses the results of 20,000 examinations where “the average time of the persistence of sweat and sweat-grease fingerprint traces on different surfaces” and in different environments were documented. “A video comparator is used to analyze the picture of fingerprint traces” and certain “characteristic properties for the stages of the ageing process” are examined. These physical properties are then compared to those in the database, and a “probable time” that the prints were deposited is given [6].
Another example of experiments to determine the age of a latent print was reported in California in 1985. An aluminum can that was found at an outdoor homicide scene was processed with magnetic powder, and an identifiable fingerprint “popped out” [7]. An experiment was conducted that involved the placement of latent prints containing different ratios of relevant contaminants on test cans and the recreation of the environmental factors and questioned exposure times in effect at the crime scene. Testimony in court hinged upon the way in which the evidence prints developed, resulting in the opinion that the can could not have been at the crime scene for more than 24 hours [8]. In a case report published later, the time frame was expanded from 24 hours to between 24 and 48 hours [7]. This conclusion was met with opposition because, among other variables, factors including the “composition of the latent print residue were only partially recognized and addressed in a limited manner” [9].
Another method of latent fingerprint age determination involves measuring chemical changes within the latent residue. In 1980, Menzel studied the difference in fluorescence properties of “fresh” and “old” prints. He noted a red-shift of the fluorescence in prints of different ages, but because of variable initial fluorescence of many of the prints, no quantitative conclusions could be reached [10]. In a study conducted in 1980, Almog noted a similar phenomenon: the quality of “charred” prints decreased with time but was also dependent on the initial quality of the print as determined by its donor [11]. Charles Midkiff emphasized that “if there is one point on which researchers in the field agree it is that far and away the most significant fact in the permanence and subsequent development of any ‘aged’ print is its initial quality”. Regarding age determinations in Poland, he further stated, “I have considerable concern that applying data from the ‘average print’ from a database represents a giant step out of the real world.” [12]
One of the most significant problems in the quest for an accurate method of age determination is the fact that, although fairly rare, there are shocking instances of relatively old latent prints developing in a manner previously thought unlikely. In 1983, two fingerprints were developed from the point of entry of a burglary. The suspect was eventually identified and convicted of the crime. More than a year later, investigators responded to the same scene for a new burglary. Two fingerprints were developed from the point of entry and were identified as having been made by the same individual as before. The problem came when investigators discovered that the suspect was still in jail for the prior conviction. The latent lift from the original crime was superimposed with the lift made at a later date, and they were found to be identical in every detail [13]. Naturally, the prints developed in 1984 had survived even after being lifted more than a year earlier. In a similar case, the same latent prints on the exterior of a window were developed two years later [14]. More recently, latent prints were lifted a second time from a window known to have been sprayed with a water hose three months earlier [15]. The detective in the latter case recalled that there was no visible indication of powder residue from the first visit.
In a more recent example, prints were developed with ninhydrin on documents known to be over l00 years old. In 1892, control measurements were taken of full-blooded Apache Indians for cross-cultural comparison. On the back of the eight inch by eight inch card used to record the information, an outline of the subject’s hand was made. These cards were recently donated for experimentation with different methods of ninhydrin processing. The process that seemed to work best involved steaming the documents first, then dipping them in ninhydrin. Using this technique, ridge detail suitable for comparison purposes was developed on an overwhelming 70% of the documents processed [16].
Examiners in the field know that latent prints are affected by many different factors. However, the intricacies of their combined effects may never be fully understood. Subject factors include stress, metabolism, diet, health, age, sex, occupation, quantity and quality of finger contamination, and so forth. Transfer conditions include the surface texture, physio-chemical structure, curvature, temperature, temperature difference, pressure, contact time, and so forth. Some environmental factors include temperature, humidity, ultraviolet and other radiation, dust, precipitation, condensation, friction (handling or other natural movement), air circulation, atmospheric contamination, and so forth. To reliably test the effects of one variable, all others must be held constant. This is virtually impossible to achieve with so many different factors, many of which are frequently unknown to even the most experienced examiners. Even if the effects of changing just three separate factors could be fully understood and documented, the effects of exposure to variables of all three at the same time would not necessarily be predictable.
If an accurate method of latent print age determination is to be developed, accepted, and put into widespread use, one of two roads must be followed. Either the method must account for all relevant factors affecting the latent print, including its initial quality (e.g., composition, viscosity, contamination, etc.), or more realistically, it must hinge on a constituent(s) in the print that is not significantly affected by such factors. If a compound in latent print residue can be identified which deteriorates with time, and is not significantly affected by environmental factors, then it might be possible to establish, with relative accuracy, the age of the deposit.
As compounds deteriorate and react with their environment, isomers (compounds that have the same number and kind of molecules but differing in arrangement) of those compounds are sometimes formed. Perhaps if a constituent of natural finger perspiration can be found that follows relatively predictable isomerism, and does so mainly with time, then testing can be applied to measure these changes. In 1975, Olsen explained how the concept of racemization (the conversion of an optically active molecule into an optically inactive form by creating an equal mixture of the molecule and its mirror image ), similar to isomerism, might provide insight to the age of latent print residue [17]. Fresh amino acids in a solution affect polarized light differently than deteriorated amino acids in the same solution. Olsen suggests that this phenomenon could possibly be adapted to latent prints by researching differences over time in the optical activity of chemical compounds in perspiration.
The first step toward an accurate method of latent print age determination would be to identify the types and amounts of all trace constituents found in natural fingerprint residue. In the 1970s and 1980s, Robert D. Olsen, Sr. conducted some research toward this goal, but because of the lack of a high temperature column for the gas chromatograph being used, satisfactory results could not be achieved [18, 19]. The Pacific Northwest National Laboratory recently completed an advanced fingerprint analysis project to identify which chemical compounds in natural fingerprint residue remained stable over time. Although the goal of the study revolved around enhanced latent print visualization through new chemical reagents, a major thrust of this work was to gain insight into how fingerprint residue changes with time. Most of the unsaturated lipids rapidly diminished, leaving behind saturated compounds and wax esters [20, 21]. Although these compounds may not be effective receptors for chemical reagents, it is possible that further research would offer insight into the usefulness of these heavier compounds for latent print age determination [22].
Another approach in the quest for improved visualization reagents involves analysis of the products formed during the degradation of natural fingerprint residue. The Savannah River Technical Center recently focused on the oxidation process of lipids, identifying hydroperoxides as a possible receptor for new chemiluminescent latent print development techniques. Again, the aim of this study was not directly related to latent print age determination, but the results of this research could be taken a step further in that direction [21].
Of course many factors, especially ultraviolet radiation, significantly affect the breakdown of even the most stable compounds of latent print residue. Recent collaborative efforts by the Home Office Forensic Science Service in London and the United States Secret Service confirm that there are significant differences in decomposition rates for samples in different lighting conditions [21, 22]. The identification of a suitable compound for latent print age determination will probably hinge on intrinsic changes within the residue that are not significantly affected by differences in most environmental factors. In other words, the increased presence or absence of the compound itself should be mostly independent of environment. If (or when) a suitable compound(s) is identified and isolated, its presence (or absence) over time could be documented and the results, if reliable, could be related to the degree of change of the same constituent, if found in a questioned latent print. Issues such as sampling procedures and processing conf licts could be addressed at a later time.
Currently, there is no analytical method for age determination. It seems that the identification and evaluation of components in perspiration which change with time could offer the most promise. Only continued research will determine whether latent print age determination lies hidden, waiting to be discovered, in the change in properties of the more stable compounds found in natural fingerprint residue. Because of the relevance of the issue in criminal investigations, the search goes on. Until then, examiners should handle the issue very carefully. After an extensive study of related articles, Charles Midkiff warned that “speculation or court testimony concerning the time when a latent print was placed is fraught with danger and may be hazardous to the reputation of the examiner.” [23]
*From the Journal of Forensic Identification Vol. 53, No. 1, January/February 2003
The Official Publication of the International Association for Identification
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