Unvalidated or Improper Forensic Science

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Forensic Science refers to the application of a broad spectrum of sciences in an attempt to answer questions of interest to a legal system. Forensic science has shaped the world of justice, fuelling crime investigations and signifying the progress of modern technology. Forensics may be used in relation to a criminal or civil action. Forensic science may conver for example modern computer/clay facial reconstruction, DNA fingerprinting, Autopsy techniques, forensic anthropology, toxicology and much more.

Types of forensic evidence

There are numerous types of forensic evidence. These can include fingerprints, DNA and hair. There are many other types of forensic evidence, yet these 3 are some of the most common types which produce unvalidated or improper evidence.


Fingerprint identification is utilized at many levels of the process. This includes:

1) Warrants and extradition. Police officers and jailors use fingerprint identification evidence to confirm a suspect's identity and to facilitate arrest

2) Charging decisions. Positive and negative conclusions on fingerprint identification evidence are evaluated to determine the strength of the case and the appropriate charges to file;

3) Jury trials. Latent fingerprint examiners, which are the prosecution's expert evidence use fingerprint evidence to conclude whether the fingerprints of the accused match those found at the crime scene

4) Appeals. The existence of fingerprint identification evidence is used to bolster the prosecution's argument that the jury's verdict was appropriate and that any other alleged error at trial should be viewed as harmless error considering the strong weight of the fingerprint identification evidence.

Types of fingerprints

There are two types of fingerprints namely-

  • 'Rolled' or 'inked' prints: obtained by individuals inking their fingers and rolling each fingertip from edge to edge on paper - these are also called 'known fingerprints' because the identity of the person is known when they are taken and
  • Latent fingerprints- obtained by using fingerprint powder to make the latent print visible. Once the latent print is made visible, tape is used to lift the latent print from its original surface onto a lift card. These lift cards are examined by fingerprint identification experts who compare the friction ridge detail in the known print. Both types are utilized in the criminal justice system

Both types of fingerprints are used in the criminal justice system

Points of match

Fingerprint experts reach a conclusion as to whether the fingerprints found at the crime scene match those of the accused on the basis of 'matching points'.

At the moment there are no universal standards of matching points. Examiners historically have employed identification standards ranging from eight to sixteen matching characteristics, or "points of similarity.". Yet, the FBI has stated that there should be no minimum standard and that the determination of whether there is a sufficient basis for an identification should be left to the subjective judgment of the individual examiner. The same is applied in the United Kingdom. On the contrary, other countries have set standards. For example, Australia has a minimum standard of twelve matching ridge characteristics whereas France and Italy have sixteen.

Accuracy of fingerprints

The assumption that fingerprint evidence is one hundred percent accurate in determining an individual's identity is a fact that NEITHER science NOR law can prove with any certainty because the question has never been posed or empirically studied.

Even if one assumes that it is true that no two people in the world have the same fingerprint, this argument is logically flawed when it comes to the identification of latent fingerprint fragments. It simply does not follow from this that a fingerprint examiner can reliably make an identification from a small distorted fingerprint fragment that might reveal only a small number of ridge characteristics.

The current legal debate of fingerprint identification evidence is NOT the physiology of fingerprints, i.e the uniqueness of the mark. The issue is whether fingerprint examiners can accurately and conclusively determine the identity of an incriminating latent print found at a crime scene. This is because fingerprint experts must rely on the naked eye to reach a conclusion. This is clearly very problematic and it reinforces the argument that fingerprint identification evidence can be unreliable.

Data of erroneous fingerprint identification

There is a worrying number of examples involving erroneous fingerprint identification.

  • Cowans case

Cowans was convicted of armed assault with intent to murder in 1998 after being accused of shooting a police officer. He was linked to the crime by the testimony of two eyewitnesses, one being the victim, but also from a fingerprint found on a mug from which the assailant had drunk. Fingerprint experts testified that it was Cowan's fingerprint. He was sentenced to 35 years of imprisonment. When he managed to collect enough money, he had the evidence tested by DNA. The DNA did not match his, yet he had already served SIX YEARS in prison before he was eventually released.

  • Photographs of ten pairs of latent and inked fingerprints were sent out to fingerprint bureaus in England and Wales requesting that experts with ten or more years of experience undertake the ten comparisons independently of each other. Nine of the pairs that were supplied were taken from past casework of Scotland Yard. Six of these pairs were properly identifiable to one another, while the other three were considered borderline cases. The tenth pair provided by the researchers consisted of two prints that were made by different fingers. The examiners were asked to decide whether each of the pairs were identifiable and, if so, the number of corresponding points of similarity that could be seen. The variation in the 130 responses was extraordinary. For example, the number of points of comparison that the examiners reported in one of the pairs ranged from ten to forty. There was also considerable disagreement as to whether identifications could properly be effectuated. On one of the pairs, 44% of the examiners found that an identification could be made, while 56% said that it could not
  • Proficiency Tests - While these exams do not constitute controlled scientific studies, they nevertheless do provide some indication of the proficiency, or lack thereof, of examiners.

1. CTS 1995 Latent Fingerprint Proficiency Test- Of the 156 examiners who participated, only sixty-eight (44%) were able to correctly identify the five latent prints that should have been identified, and to correctly note the two elimination latent prints that were not to be identified. Even more significantly, thirty-four of these examiners (22%) made erroneous identifications on one or more of the questioned prints for a total of forty-eight misidentifications.

2. CTS 2007 Latent Fingerprint Proficiency Test- The test materials included two latent prints produced by people whose known prints were not provided. Yet four examiners incorrectly matched one of the latent prints to one of the known's, three matched a latent to an innocent suspect, and a fourth one matched a latent to an innocent bank employee.

There is a clear lack of universal standards both in matching points but also in what experts are looking for when comparing fingerprints. There are varying beliefs amongst experts as to the number, nomenclature, and frequency of the standard ridge characteristics. In addition, another worrying fact is that there are no mandatory qualifications to become a fingerprint examiner. Even though the Scientific Working Group on Friction Ridge Analysis, Study, and Technology (SWGFAST) adopted quality assurance guidelines for latent print examination in 1997, these guidelines are optional, not mandatory. Lastly, it has been established that fingerprint identification Is based upon the subjective decision of the examiner, NOT science. Although computers might be used to initially retrieve the known fingerprint records to compare to the latents, this merely "provides a list of candidates . . . [but the] direct comparisons are made by a fingerprint examiner."


The second type of forensic evidence which will be analyzed in this course is DNA.

We all possess specific DNA sequences, which act as genetic fingerprints. DNA is found in every cell of a human - blood, hair, skin, etc- often left at the scene of the crime. They are also left by the victim on the body of the perpetrator. No one's DNA is identical to anyone else's (excluding the case of identical siblings), so if a sample matches the sample taken from the scene of the crime, there is a high probability that they originate from the same person.

Process of DNA testing

Some basic steps are performed during DNA testing. These include:

1) the isolation of the DNA from an evidence sample which contains unknown DNA, and at a later stage, the isolation of DNA from a sample from a known individual

2) the processing of the DNA - Under this step, the DNA is extracted from its biological source material. After isolating the DNA from its cells, specific regions (loci) are copied with a technique known as the polymerase chain reaction (PCR). PCR produces millions of copies for each DNA segment of interest and therefore permits very small amounts of DNA to be examined. Multiple STR loci can be examined at the same time (The variability in STR regions (loci) is used to distinguish one DNA profile from another.

3) the determination of the DNA test results, from specific regions of the DNA and

4) the comparison and interpretation of the results from the unknown and known samples to determine whether the known individual is included or excluded as a possible source of the DNA.

Despite the fact that DNA is unique to each individual, as a defense lawyer you must always be cautious. Always have in mind that DNA profiling is a very complex affair, with many different technical stages. At any one of these stages problems may occur that could invalidate DNA profiling evidence. These may include problems with the quality, quantity and purity of the DNA possessed.

  • Quality: A problem with DNA evidence may result because of its quality. If the DNA sample has been left in adverse conditions for even a period of 24 hours, the sample may become degraded, and the evidence would no longer be able to be tested (i.e moist, warm conditions). The bands will not be clear, but will be smeared. Incidentally, when DNA is submitted as evidence, one must ensure that the test showing that it is not degraded must also be admitted.
  • Quantity: The quantity of the DNA sample may cause problems, It is very difficult to create a DNA profile if the sample is not very big. In addition, if the sample is too small it may be used up entirely by the prosecution, leaving the defence with no ability to carry out their own tests.
  • Purity: Another possible problem that may occur is the contamination of the DNA sample. A sample obtained for example by a bloodstain at the scene of the crime, may not be a pure sample, but might actually be a mixture of the victim's blood and that of the assailant's. The impurity of the sample may also come about from bacterial DNA at the crime scene, or even from the laboratory.

Data of erroneous DNA testing

  • In 2001, Arizona state crime lab analyst Kathryn Troyer was running tests when she found two felons with remarkably similar genetic profiles. They matched at 9 of the 13 locations on chromosomes, or loci, commonly used to distinguish people. Despite the fact that the FBI estimated the odds of finding unrelated people sharing those genetic markers to be 1 in 113 billion, she found the men to be unrelated and of different races, one was black and the other white. - Since then, Troyer found dozens of similar 'matches'.
  • In the US case of GILBERT ALEJANDRO, the forensic expert testified that he had conducted DNA testing and obtained results inculpating Alejandro. He referred to the patterns as being 'identical' to those of Alejandro and that they could only have originated from him. He gave no random match criteria for this DNA inclusion, but falsely told the jury that "DNA typing is a hundred percent identity as to whether a blood or body fluid may have originated from a particular donor or not." A subsequent internal inquiry concluded that he had at best compared only partial banding pattern results visually; LATER TESTS EXCLUDED ALEJANDRO
  • Another invalid DNA testimony can be seen in the case of STATE OF TEXAS v. JOSIAH SUTTON. The victim was raped by two men. Semen was found in the vaginal swab and on the stain removed from the back seat where the rape occurred. The official report presented invalid DNA results. The raw data and the analyst's bench notes indicated that whereas the vaginal sample reflected a mixture of the victim's DNA and DNA from two male donors, the semen stain on the car seat suggested it came from one man only and that the lone male could not be Sutton. Although Sutton was excluded as the source of the car seat semen stain, that conclusion was not mentioned in the official report nor in the analyst's testimony at trial.

If the back seat stain was considered in conjunction with the vaginal swab data, Sutton could probably have been ruled out as one of the rapists.

DNA evidence can provide a powerful link between a defendant, a crime scene, and a victim. However, it is crucial that lawyers, factfinders, and experts understand the weaknesses of DNA evidence, the meaning of a reported match as well as the conditions under which it should more and less impact on judgments.


The third type of forensic evidence that we will look at is hair. Hair is one of the most common types of trace evidence. It varies extremely among both individuals and racial populations. Hair may in some cases rule out certain populations or help identify an unknown victim. Transfer of hair from a victim to a suspect or vice versa may substantially raise the probability that the victim and perpetrator were in contact.

Hair Microscopy

The variability of hair characteristics can be seen through the use of comparison microscopy. Hair microscopy is a two-step process. Firstly examiners identify the questioned hairs and once this has been concluded, they compare the questioned and known hair, i.e hair found at the crime scene. The purpose for this examination is to determine whether two or more individuals could have come into contact. This associative evidence is particularly helpful in crimes of violence, like homicide and sexual assault where physical contact may have occurred. Crimes like burglary typically involve the recovery of debris and articles of clothing which may also contain hairs useful for identifying suspects.

The hair examination process involves many different steps:

a) The examiner determines whether the hair in question originated from an animal or a human being. If the hair originated from an animal, it is possible to further identify it to a particular type of animal. Although certain hairs can be attributed to species, it is not possible to identify hairs to a specific animal to the exclusion of other similar animals.

b) The examiner conducts a Racial Determination- A human hair can be associated with a particular racial group based on established models for each group. Forensic examiners differentiate between hairs of Caucasoid (European ancestry), Mongoloid (Asian ancestry), and Negroid (African ancestry) origin. Head hairs are generally considered best for determining race. Racial determination from the microscopic examination of head hairs from infants, however, can be difficult, and hairs from individuals of mixed racial ancestry may possess microscopic characteristics attributed to more than one racial group). Lastly,

c) The examiner may be able to determine the age and sex of the individual- The age of an individual cannot be determined definitively, however, the microscopic appearance of certain human hairs, such as those of infants and elderly individuals, may provide a general indication of age. The hairs of infants, for example, are generally finer and less distinctive in microscopic appearance. As individuals age, hair can undergo pigment loss and changes in the configuration of the hair shaft to become much finer and more variable in diameter. Although the sex of an individual is difficult to determine from microscopic examination, longer, treated hairs are more frequently encountered in female individuals. Sex can be determined from a forcibly removed hair (with tissue), but this is not routinely done.

Data of erroneous hair microscopy

Hair microscopy is not 100% accurate. Forensic hair evidence has increasingly been scrutinized due to studies indicating high error rates.

As the FBI noted in its 1984 handbook, microscopic hair examination is "not positive evidence." (For further information see Fed. Bureau of Investigation, Handbook of Forensic Science. 33(1984) )

Furthermore The National Research Council has explained:

"Although hair examiners can associate a hair with racial characteristics and body source (trunk, head, or pubic area) the variations among hairs on a given person make definitive association of a single hair with an individual problematic. The microscopic comparison of hairs is also subjective and can lead to differences of opinion among equally qualified experts" (For further info see Comm. on DNA Tech. in Forensic Sci. Nat'l Research Council, DNA Technology)

Though there is not, and never has been, any statistical basis for hair comparison, some experts have fabricated frequencies and probabilities based on their own undocumented estimates, rather than any reliable empirical data. An example of such a testimony can be seen in the US case of STATE OF MONTANA v. JIMMY RAY BROMGARD.

Hair evidence should never be used as the so called "smoking gun" which would prove a person's guilt. The information obtained from hair is expressed in terms of probabilities of a match rather than an absolute match.

It must however be noted that DNA testing of the mitochondria, or when the hair roots are present, of the nucleus, has now supplanted microscopic hair comparison in many cases.

Additional factors undermining forensic evidence

  • Issue with factfinder - If we are dealing with a jurisdiction where the jury is deciding if the accused is guilty and whether the evidence presented proves this, there might be a problem. The jury does not have the expertise to fully understand the forensic evidence, thus the expert must write a detailed but understandable report and present it to them. This can be problematic because by simplifying the case for the jury to understand, the expert may omit a vital piece of evidence. Throughout the investigation, the forensic expert may not know the details of the case, and so there is a possibility that he does not know which piece of information discovered is crucial to the case. If something of importance is not extracted from the expert during questioning, vital information may never be found out, until an appeal is launched.
  • Another problem that arises is that the forensic experts themselves are employed by either the prosecution or defense. Therefore, this may introduce bias into the case, and so only certain types of evidence beneficial to their side will be investigated. Also, there is a high probability that forensic evidence will be beneficial to the prosecution because the police, when collecting evidence, often have a suspect in mind, and so the forensic scientist is only asked to confirm the suspicions of the police. The other problem with this method is that the police may tend to collect evidence that will uphold their theory that their suspect is the correct person.

See Causes of Wrongful Convictions