Under the Microscope: Legal Challenges to Fingerprints and DNA as Methods of Forensic Identification
Wise, International Review of Law, Computers, & Technology, 2004
Wise discusses the advent of both fingerprint and DNA technology, and addresses the legal challenges they’ve faced as well as how the determination of legal validity will affect emerging biometric identification means. He notes that Galton, a 19th century scientist, proclaimed that fingerprints were unique to each individual and permanent, as well as developing a system to identify the unique characteristics of a fingerprint (called Galton points). Sir Edward Henry, a contemporary of Galton took an interest in fingerprints, and with consultation from Galton, developed the Henry Classification System to catalog fingerprint data, thus ushering in the modern era of fingerprint science The classification system is still used today and has enjoyed worldwide acceptance and use.
Challenges to the admissibility of latent prints are based on established standards of evidence admissibility. The 1923 case, Frye vs the United States, originally set a standard for expert testimony (in this case, in the admissibility of lie detector results), in that experts should only testify if their testimony is based on “general acceptance” in the scientific community. This standard was widely utilized until the 1993 case, Daubert vs Merrel Dow Pharmaceuticals. This case set out new, comprehensive criteria which included, whether the scientific theory has been tested, whether it has been subject to peer review and publication, whether it has a known error rate, whether it has widespread acceptance, and whether there are operating standards. It was from the establishment of the Daubert standard that questions about the admissibility of latent prints arose.
In 1999, the case United States vs Byron Mitchell, was the first to challenge the admissibility of fingerprint evidence, and while the judge dismissed the challenge, the issue came up again in 2002, with United States vs Carlos Ivan Llera Plaza. The judge ruled that while the analyst may testify to some components of the analysis such as the methodology and the number of matching points between the latent print evidence and the defendant, he would not be allowed to testify as to whether the evidence matched the print of the defendant. The judge ruled latent print analysis did not meet the Daubert standard, because of a lack of known error rate and differing standards on how many Galton points signifies a match. However, the judge later reversed his ruling after reviewing US and UK data, concluding that there was a clearly established standard of analysis in the scientific community to satisfy the Daubert standard. Since the Mitchell case there have been 40 challenges to the admissibility of latent print evidence but in all the cases, fingerprint evidence was allowed.
In 1984, Dr. Alec Jeffreys, a researcher studying gene structures determined that DNA sequences are unique to individuals and two years later was helping law enforcement utilize DNA to identify a serial killer in the UK., which both exonerated an innocent man and was able to match DNA from a suspect to the evidence. Jeffreys’ RFLP method has been refined since then to an STR technique where only a small amount of DNA is required for analysis, as well as developing the use of mitochondrial DNA testing that utilizes a different methodology that works especially well on degraded DNA evidence, and in cases requiring the identification of family members.
The first challenge to RFLP DNA evidence occurred in the late 80’s in the case of United States vs Bonds. The District Court ruled that the DNA evidence was admissible based on the “general acceptance” standard of Frye, however the US Court of Appeals ruled in 1993 that the DNA evidence was admissible under the Daubert standard, despite the laboratory not conducting external blind proficiency tests or referencing a known error rate. The judge determined that if the scientific community was accepting of the technology, it must also then be accepting of the error rate as well. RFLP DNA analysis was also challenged in the NY case of the People vs Castro. In this case, the court used a three prong Frye test to determine if the theory, and its techniques and experiments, could produce reliable results that were generally accepted by the scientific community, and whether the laboratory performed the accepted scientific techniques in analyzing the sample in the particular case. The court ruled the first two prongs were met,, in that the science was sound, but that the laboratory failed to the meet the accepted scientific testing standards.
STR DNA analysis was also challenged in many courts. For example in State vs Traylor, although Traylor argued the validity of commercial DNA tests are unknown because of the use of proprietary regents used in the analysis, the MN Supreme Court, in 2003, ruled that the DNA Advisory Board and its established guidelines developed by the FBI, met the admissibility criteria and validated the science. While challenges to mtDNA are relatively new to the courts, recent challenges have established that mtDNA analysis constitutes a “scientific knowledge based on reliable methods and principles”.
Newer DNA analysis technology, like Low Copy Number (LCN), while accepted, may face challenges as well. LCN DNA techniques can utilize very small samples of DNA and produce 17 billion copies to allow for analysis. However the concern is that as the original sample gets smaller in this process, any contamination in the sample will have a larger effect on the results of the analysis. Other concerns are the transfer of LCN DNA from casual contact and the lack of scientific evidence available as to how long this casual contact DNA could remain. While “shedder indexes” are being investigated to determine the rate at which an individual donates potential DNA material (i.e. skin cells, hair, sweat), researchers have reported that DNA can be detected after transfer to an object for nearly three months in some cases and in one case for 2 years. Even more importantly, with such a small sample size of LCN DNA, there typically is no material left over after testing for an outside source to run its own analysis and produce data. The FBI, with the exception of the limited application in human remains identification, remains skeptical of LCN DNA. Their official position is that any profiles obtained from LCN DNA should not be entered into the Combined DNA Index\System (CODIS) database of offenders and suspects. They also issued a caution against a rush to re-examine old cases on the hopes that LCN DNA would offer better analysis or change a verdict, mainly because of the risk of evidence contamination from repeated handling.
While fingerprints, and now DNA, are classic biometric measures, new measures of identification are being developed like ear prints, facial and voice recognition, iris, retina, and vein patterns, and hand geometry. The newer technologies will likely face challenges as they are introduced into the courtroom. Part of what drove the acceptance of latent print admissibility is that the scientific standard had been developed over a 100 years of use. Newer technologies will need to demonstrate that they can meet the Frye or Daubert standards and this also puts a burden on the judiciary, highlighting the situation created by Daubert,which requires judges, who are often not trained in the sciences, to act as gatekeepers of evidence admissibility. Even if these new technologies become “generally accepted”, criminal defense attorneys can still criticize the application of the method by the individual laboratory, and if the laboratory demonstrates they meet the scientific standards, the training or performance of the individual analyst can still be called into question.
Wise, J. (2004). Under the microscope: Legal challenges to fingerprints and DNA as methods of forensic identification. International Review of Law, Computers & Technology, 18(3), 425-434.
Recognizing the challenges faced in determining admissibility is important for defense attorneys as well as prosecutors, criminalists, and detectives. Being able to present solid, scientific based identifying evidence is crucial for prosecutions, as is producing accurate evidence data from other sources at the crime scene. Knock and Davison developed a methodology that they believe will produced more detailed, accurate information on the source of blood stain evidence.
Predicting the Position of the Source of Blood Stains for Angled Impacts
Knock & Davison, Journal of Forensic Sciences, 2007
The authors note that in the field determining the source of blood splatter evidence typically involves the “stringing method. As the authors explain “This technique uses the fact that the width to length ratio of a blood stain is approximately related to its impact angle. Using the calculated angle of impact, a straight line is drawn back from the stain along the line of the impact angle. Where the lines from several stains intersect is assumed to be the source of the stain.” They also note though that the effect of gravity on the flight path of blood droplets isn’t taken into account in making this determination. Knock and Davison experimented by dropping blood droplets of varying sizes at different height and angles against a hard surface. From this data, they produced one equation relating stain size to drop size and velocity for all impact angles, and a second equation, relating the number of spines (blood fingers extending from the center of the drop caused by impact) to drop size, velocity, and surface slope for all impact angles. The authors demonstrated that by combining these two equations, impact velocity can be accurately calculated and thus the true position of the blood stain’s source.
Knock, C., & Davison, M. (2007). Predicting the position of the source of blood stains for angled impacts. Journal of forensic sciences, 52(5), 1044-1049.
Revising and refining scientific methodology can improve the forensic investigative ability of detectives and criminalists but its also necessary to re-evaluate perceptions we hold about certain criminal activity and the perpetrators. Ferguson, et al reminds us that conventional wisdom is not always correct and that the analysis of data is necessary for the proper assessment of contributing and causal behavior in determining who might be at risk for perpetrating a school shooting.
Psychological Profiles of School Shooters: Positive Directions and One Big Wrong Turn
Ferguson, Coulson, & Barnett, Journal of Police Crisis Negotiations, 2011
The authors contend that the stereotype presented by the media and typologies produced both by the American Psychiatric Association and the FBI are simply inaccurate, or too overly broad and vague, to be of use. While conceding that first hand data from shooters who often die in the incident is hard to come by, a more evidence based typology can be utilized.
School shooters are typically portrayed as loners, involved in the Goth subculture or other out-groups, who enjoy violent video games, were bullied, and had disruptive or negligent home lives. When school shootings increased in the’90’s the public, academics, politicians, and activists demanded answers, despite their relative rarity and the overall general decline of youth violence.
In 1999, the FBI provided a threat assessment profile for school shooters cautioning against its use other than in assessing the credibility of a threat already made by an individual. Some criteria seem reasonable like “injustice collector, dehumanizes others, and lacks empathy” while others were vague in definition like an “unreasonable interest in sensational violence” and overly broad like “a failed love relationship, a sense of superiority, exaggerated need for attention, externalizes blame, closed social group, a fascination with violence filled entertainment”.
As of 2010 the APA maintained a warning signs list for serious youth violence including obvious signs like “enjoying hurting animals, detailed plans to commit acts of violence, and announcing threats or plans for hurting others” but like the FBI’s threat assessment, others are vague in definition like “frequent physical fighting” while others could apply to great numbers of mentally-well juveniles like, “feeling rejected or alone, poor school performance, and access to or a fascination with weapons, especially firearms”.as well as including ideas that have been discredited by research like “violence is a learned behavior” and linking violent media, like video games, with violent behavior.
These attempts at recognizing school shooters will result in over-identification and misidentification and while empirical evidence on characteristics of school shooters is scant, a 2002 report from the Secret Service and Dept. of Education does provide a more data derived (albeit descriptive) picture of school shooters. The reported analyzed 37 attacks, involving 41 perpetrators from 1974 to 2000 and utilized school and court records, mental health and legal documents as well as interviews with the ten surviving perpetrators. The report made clear that with the wide difference among perpetrators that no profile for school shooters existed, though there were some features that tended to be more widespread. The report also demonstrated that the stereotypical school shooter image is inaccurate. The SS/DOE report found that video game playing was relatively low, only 15% expressed “some interest in violent video games” and just 59% expressed “some interest in violent media in other forms”, with the authors noting these figures are lower than those found for non-shooter males in other studies. However, 37% were exposed to media violence through their own poems, essays, and journals.
Social isolation was not found to be common with school shooters. Most had friends, 41% belonged to a mainstream social groups, (27% were part of fringe groups but also had friends). In categories that were not mutually exclusive, only 12% had no friends and 34% were described as loners. School and family background also did not figure prominently into school shooters’ behaviors. However mental health issues were a factor. 98% of perpetrators experienced some kind of major loss right before the incident, 78% had a history of suicide attempts or ideation, 71% percent of then perceived themselves as wronged, bullied, or persecuted by others, and 61% had a documented history of significant depression. However very few of the perpetrators had received any mental health care in the past, suggesting a failure of our mental health system that has contributed to these incidents, Two prominent warning signs noted in the SS/DOE report were that 81% of perpetrators warned an uninvolved person prior to the attack and that 93% had already engaged in behaviors that alarmed peers, teachers, parents, or mental health professionals.
These factors have been identified in research on adult perpetrators of mass homicide as well as figuring into youth violence in general. Ferguson noted his upcoming study revealed that violent media was not a factor in youth violence, however current levels of depressive symptoms coupled with antisocial personality traits, were highly predictive of youth violence. The authors suggest that reducing school shootings should focus on preventative measures however, reform in addressing mental health needs is long overdue, and funding for adequate at-risk youth and adults services will be slow in coming. They also note that because of the likelihood that perpetrators may signal their violent intent before the action, that prevention can take the form of peers acting upon what they hear or see and informing law enforcement or school officials.
Ferguson, C. J., Coulson, M., & Barnett, J. (2011). Psychological profiles of school shooters: Positive directions and one big wrong turn. Journal of Police Crisis Negotiations, 11(2), 141-158.
Officers are often called upon to confront resistant and/or violent individuals and by necessity have a choice of non-lethal options they can employ in these encounters. One technique that has caused controversy over its application and the potential for harm to suspects is the chokehold, both historically and as recently as last year. Below, Dr. Koiwai examines factors that may be contributing to deaths in the application of choke holds.
Deaths Allegedly Caused by the Use of “Choke Holds” (Shime-Waza)
Koiwai, Journal of Forensic Sciences, 1987
Author Koiwai, MD, stated that the chokehold technique used by police officers is the same chokehold (Shime-Waze) used in Judo. Yet while officers have been involved in the deaths of suspects following application of the hold, Koiwai notes that since the sport of Judo was established in 1882, there have been no fatalities associated with the use of the hold in Judo.
Koiwai briefly discusses the control techniques used by the police which are similar to Judo chokeholds, including the carotid control hold (fig. 1) the locked carotid control hold (fig 2), as well as the bar arm control hold, where the left hand is placed on the back of the subject’s head forcing it down. All of these holds are finished by using the hold to take the subject down to a seated position and applying the hold until the subject becomes unconscious or ceases resisting.
Koiwai examined the autopsy reports of 13 cases between 1975-1985 which involved a law enforcement chokehold being applied. The decedents were males, Black and White, between the ages of 19 and 58, though the majority were under 40, and their weight ranged from 120-220 pounds, though in only one case did the decedent weigh over 170 pounds. While in all but one case the decedents were violently resisting arrest, which necessitated the use of the chokehold, the case narratives indicate that in six of the cases, the decedents were very violent and combative. In three of the 13 cases, acute intoxication from alcohol or drugs was involved, two other cases involved decedents suffering from psychosis, as well as the findings that in three other cases, pre-existing heart conditions contributed to the death. In almost all the cases medical attention was provided in a timely matter, though in all the cases, asphyxiation was a primary factor, including in some cases, aspiration of vomit, and brain death from oxygen deprivation.
In all 13 cases, the author noted evidence of injuries to the structures of the neck ranging from bruises, lacerations, hemorrhages, and vascular compression, as well as fractures of the cartilage of the neck in five cases, and intervertebral discs in one case. Submucosal or mucosae injuries are noted in the larynx in five cases. All these findings indicate that tremendous force was exerted on the necks of the decedents. Koiwai noted that only a relatively small amount of pressure is necessary to close off the carotid arteries and that unconsciousness should occur in only 10-20 seconds, with regaining consciousness occurring in about the same time length. Koiwai stated that the force applied to collapse the airway, as occurred in these cases, is 6 times greater than necessary to effectively apply a chokehold, which resulted in the injuries seen in the autopsy reports. Properly applied the chokehold puts pressure on the superior carotid triangle, closing off the carotid artery but leaving the vertebral artery unobstructed. (fig 5) Completely obstructing the blood flow to the brain or asphyxia by closure of the trachea can lead to irreversible damage or death.
Koiwai suggests that police department training manuals should emphasize that control holds should be used only when necessary to stop a suspect’s resistance and not necessarily to cause unconsciousness. If police officers are to use the choke holds to subdue violent suspects as a last resort, they should be properly trained and supervised by trained, certified judo instructors to ensure that there will be less misuse or abuse of the technique which when used improperly results in fatalities. These fatalities could be reduced if (1) choke holds are taught by trained and certified instructors (2) if officers become familiar with the anatomical structures of the neck and where the pressure is to be applied (carotid triangle), (3) if they understand the physiology of choking, in that only a small amount of pressure is needed to cause unconsciousness; (4) if officers are taught to recognize immediately the state of unconsciousness and to release the pressure immediately, (5) learn proper resuscitation methods if unconsciousness is prolonged; and to prevent the aspiration of vomit and not to place the restrained suspect face down, (6) and keep the subject under constant observation. (7) Additionally, police training manuals should be revised to emphasize the above procedures and principles, all of which will prevent deaths from chokeholds.
Koiwai, E. K. (1987). Deaths allegedly caused by the use of “choke holds”(shime-waza). Journal of Forensic Science, 32(2), 419-432.
Police officers face challenges in recognizing when to apply force and the level of force itself. Proper training in different techniques makes for better, more professional officers, as well as decreased injuries and fatalities for suspects. However, having a means to assess officer performance when they face potentially violent encounters is crucial to understanding their behavior and decision making in those encounters. Those observations can then be used to improve officer performance and public safety as well. Vickers and Lewinski examine the differences between elite and rookie police officers in their preparation for use of a firearm in a violent confrontation.
Performing under pressure: Gaze control, decision making and shooting performance of elite and rookie police officers
Vickers & Lewinski, Human Movement Science, 2011
The authors discuss that currently most firearms training programs teach officers to focus their gaze on two locations, first on the sights of their gun, and secondly on the target before pulling the trigger. This gaze strategy works very well in training with rookies achieving high accuracy scores in initial firearms training, but once on the street and faced with a violent firearms encounter they shoot poorly, averaging between 10 and 60% accuracy. The high pressure states that shooters face tend to cause more visual fixations of a shorter duration and reduced ability to detect peripheral information.
When elite shooting athletes were studied they found that they tended to fixate on the target, and kept that sight gaze as they aligned their firearm sights with the target, rather than switching gaze from sights to target; this allowed for a longer final fixation on the target leading to greater accuracy, and the reduction of pressure, anxiety and psychological stress. The authors tested 11 elite Emergency Response Team members and 13 rookie officers nearing the end of their training period, with gaze tracking software, putting them in a role-playing scenario where they are informed a threat may appear in the area they are monitoring. An upset male enters the location and becomes increasing agitated with an individual playing the role of a receptionist. In the final two seconds of the encounter, the male quickly pivots and draws on the officer who is seven yards behind him, drawing either a gun or a cellphone. Officers were assessed on their gaze duration, gaze location, amount of gaze shifting, speed, accuracy and locations of shots fired, time involved in the unholstering, draw, aim, and fire phases, and the rate that they inhibited firing in the cellphone scenario.
Following data analysis, statistically significant differences were revealed.
| Elite Officers | Rookie Officers | |
| Hit on assailant | 74.5 % | 53.9 % |
| Decision making (fired on cellphone) | 12.3 % | 61.5 % |
| Fired before assailant | 92.5 % | 42.2% |
| High Performance (meeting all above criteria) | 75.0 % | 52.9 % |
| Fixated on more locations where gun could be concealed | 50.3 % | 30.6 % |
| Fixated on locations where gun couldn’t be concealed | 42.1 % | 51.1 % |
| Fixated on areas off the assailant | 7.6 % | 18.1 % |
| Unholstered weapon after assailant entered | 1.77 sec. avg | 6.28 sec. avg. |
Statistically significant differences were also found in the final phases of the scenario between the onset times of the different phases based on officer status.
| Onset | Elite | Rookie |
| Draw | 4.63 sec. | 6.04 sec. |
| Hold | 4.81 sec. | 6.26 sec. |
| Aim | 5.83 sec. | 6.36 sec. |
| Fire | 6.87 sec. | 6.93 sec. |
There were also statistically significant differences between elite and rookie officers in their visual fixations during the final two seconds of the scenario.
| Fixations | Elite | Rookie |
| Increased visual fixation on assailant weapon | From 18 % to 71 % | From 18 % to 34 % |
| Decreased fixation on non-weapon locations | From 78 % to 7 % | From 62 % to 16 % |
| Increased fixation on officer’s weapon to | 20 % | 39 % |
| Fixations off assailant | 4 % | 13 % |
| Final fixation on officer weapon not assailant | 32% | 84 % |
| Final fixation time on assailant before firing | .32 sec. | .27 sec |
| Final fixation time on ofcr. weapon before firing | .12 sec | .24 sec |
In reacting to the threat, rookie officers performed the final phase actions in the last second of the scenario versus elite officers who performed the actions in the last 2.5 seconds, starting the process earlier, taking more time to focus on the assailant and less time focusing on their own weapon. The elite officers’ earlier draw was also preceded by more time spent focusing on assailant weapon locations than rookies. Elite officers maintained more visual focus, drew sooner than rookies in anticipation of the threat, and thus gave themselves more time in the final aim and fire phases for increased fixation focus, which accounted for their better hit and discrimination rates. The authors stated that their results suggest that firearms training should change from a process that inadvertently teaches rookies to fixate on the sights of their own weapon first and the target second, to a type of training that establishes the line of gaze on the target from the outset, followed by alignment of the sights of the weapon to the line of gaze. This change in gaze control would lead to a longer final visual fixation duration on the target prior to pulling the trigger and should contribute to better decision making and performance. If these changes in firearm’s training were implemented, then the gaze control of novice officers should be similar to that of elite athletes and elite officers from the first day of training, which should decrease errors in decision making and improve shooting accuracy.
Vickers, J. N., & Lewinski, W. (2012). Performing under pressure: Gaze control, decision making and shooting performance of elite and rookie police officers. Human movement science, 31(1), 101-117.