Gait analysis is known as 'the systematic study of human locomotion.' Forensic gait analysis or forensic gait comparison is defined as 'the assessment and evaluation of the gait patterns and features of the person/suspect and comparing these features with the scene of crime evidence for criminal/personal identification.' In other words, forensic gait analysis may be defined as 'a contributor to the identification process rather than one of the methods of identification as individualization of the gait of a person has not yet been fully scientifically proved.' The general source or evidence for the forensic gait analysis comprises the series of footprints found at the crime scene and the closed-circuit television camera (CCTV) footage. Footprints are one of the pieces of evidence encountered at the crime scene. Footprints can be recovered in the form of bare prints, shoeprints as well as a series of imprints. Footprints can be encountered in several types of cases and crime scenes such as HBT (House Break-in and Theft), robbery, sexual assaults, hit and run, shoplifting, homicides, kidnapping, etc. The science of footprints and gait analysis is a part of an emerging sub-discipline of forensic science known as forensic podiatry. Forensic podiatry is "the application of podiatric knowledge and experience in forensic investigations. It shows the association of an individual with a scene of a crime, or to answer any other legal question concerned with the foot or footwear that requires knowledge of the functioning foot." The principles and knowledge of forensic podiatry help the investigating officers and crime scene investigators when they are involved with the foot, footwear and/or gait-related evidence at the crime scene. This knowledge can further contribute to establishing the physical or biological profile of the suspect for individualization and identification.
Meanwhile, an investigating officer is always on the look-out for evidence that will link the suspect to the scene of the crime. In recent times, gait analysis has emerged as an important parameter that can help in personal identification during forensic examinations. The advent of CCTV cameras and other means of surveillance have generated interest in the practice and research related to forensic gait analysis and its possible use in the human individualization. In 1839, in London, gait analysis entered into the court in the case of Thomas Jackson; he was identified by the witness due to his bowed left leg and walking with a limp. However, for the very first time, the forensic gait analysis was used as a means of admissible evidence/scientific evidence in the Old Bailey Central Criminal Court, London, UK, in the case of R v. Saunders by the U.K. based forensic podiatrist, Dr. Haydn Kelly. Although, the method of forensic gait analysis remains questionable as far as the reliability and accuracy are concerned. The article discusses the methods of forensic gait analysis, factors affecting the human gait, its forensic applications and its accuracy, reliability, and its admissibility in the court of law.
Human walking occurs in a specific pattern, including various stages, which is referred to as a 'gait cycle.' It mainly consists of two phases, i.e., the stance phase and the swing phase. The stance Phase constitutes five stages, namely; "initial contact, loading response, mid-stance, terminal stance, pre-swing." While the swing phase constitutes three stages, namely; "initial swing, mid-swing, terminal swing."
The dogma of forensic podiatry is to utilize the proper standardized methodology for scientific examination of every evidence. The gait pattern examination includes ACE-VR, which stands for analysis–comparison–evaluation–verification–report. Every step needs to be taken into consideration. After a thorough analysis, the findings are presented in the report format. The forensic gait analysis would depend on the type of gait pattern. The gait pattern may be classified into the following two types:
Forensic gait analysis approaches
Forensic gait analysis may be human-based/observer-based, as well as computer-based. Both the approaches are very briefly discussed below:
Forensic Gait Analysis Features/Parameters
For any traits or features to be useful for forensic purposes, it has to follow certain principles like universality, permanence, and uniqueness. While some may be grouped under class characteristics and some under individual characteristics. Even if one or two features may not be proof enough for a conclusion, but when these features are combined, it will result in a more reliable and scientifically sound result. Although it is beyond the purview of this article to detail the parameters/features used and factors affecting the forensic gait analysis, a brief account is given. Some of the features taken into consideration while performing forensic gait analysis (static as well as dynamic) that may contribute to the establishment of identity are as follows:
Another classification may include the spatial parameters, the temporal parameters, and the angular displacement parameters.
Factors affecting gait pattern and gait analysis:
Gait is a biological characteristic of a person, and the gait pattern is simply the manner or style in which a person usually walks. It is highly influenced by many factors (internal as well as external). Walking is often not a conscious behavior and can be used for differentiation if not for identification. Some of the factors that tend to affect the gait and hence the forensic gait analysis are as follows:
Including the factors mentioned above, there are few more that affect the walking pattern of an individual, such as emotional mind state, music, talking, load carriage, attire, etc. The person may try to bring in some changes in the gait, intentionally in order to escape being recognized in the footage or to escape suspicion. This artificial 'gait,' i.e., deliberate change in the gait, also needs to be considered by the forensic analyst/examiner.
According to Birch et al. the forensic gait analysis can be defined as "the identification of a person or persons by their gait or features of their gait, usually from closed-circuit television (CCTV) footage and comparison to footage of a known individual." It means the main source of comparison is the CCTV footage and other videos that can be used in the analysis process. In other words, it is the visual comparison of the videos to identify the individual based on gait patterns. This knowledge has been used in the crime scene investigation, particularly to identify the criminal or perpetrator from the characteristics of the gait pattern. Many forensic cases have been solved, and the criminals have been convicted based on forensic gait analysis throughout the world. Presently, Drs. Michael Nirenberg and Christine Miller in the USA, Dr. Nicholas Harris in Canada, and Professor Ivan Birch, Dr. Jai Saxelby, Dr. Jeremy Walker in the UK regularly practice forensic gait analysis.
Indirect forensic significance
The forensic gait analysis may additionally help in the estimation of stature and sex of the person, estimation of body weight, estimation of the number of people involved by measuring and evaluating step length/stride length if a series of footprints or gait patterns are available for analysis. The gait analysis may also help comment upon the type of footwear used, the use of any walking aid or support (like a walking stick), underlying disease/disorder/medical condition affecting the gait, etc.
The clinical gait analysis helps in the assessment and treatment of individuals with pathological and/or underlying neurological conditions that may affect their ability to walk. With the help of gait analysis, podiatrists, neurologists, and orthopedic surgeons usually diagnose the issues related to the cause of pain, such as muscles, nerves, and skeletal problems, consequently initiate the treatment for correction of the gait-related abnormalities and develop rehabilitation protocols. Gait analysis is being used in several fields, including sports science, rehabilitation and recovery medicine, kinesiology, and orthopedics.
Limitations of forensic gait analysis and criticism about its admissibility in the court of law
In the present era, due to the paradigm shift in forensic science, there is an increased focus on the reliability, accuracy, quality of evidence, and its admissibility in the court of law. Forensic gait analysis has also witnessed criticism regarding its reproducibility, reliability, lack of proper standards, and rules of forensic practice.
Gait pattern or walking pattern is highly affected by various parameters mentioned above, so it brings the investigating officer into a situation that requires consideration of several factors, which is practically not possible to identify the single suspect. Another limitation of gait pattern analysis is that we do not have databases that can be used for gait comparison. Gait pattern shows high intra-individual variability. It means that the gait of a person is highly variable on different occasions and scenarios, which makes it difficult to identify the person. Moreover, the experts are not following any prescribed standard protocol for the analysis of gait; consequently, there are variations in the methodology used for the analysis, which creates confusion amongst the judges and jury to decide the cases based on this parameter of identification. Presently, the research is being carried out in the area of automated gait recognition combined with larger & variable datasets, tested variables, and enhanced statistical evaluation of results. Despite these improvements, any form of forensic evidence without fully recommended codes of practice and standardization of procedures and having error rates in reproducibility and repeatability should be treated with caution in forensic scenarios. The forensic gait analysis remained a weak method of identification since the observation of the gait features by the experts also vary in different situations. A study conducted by the forensic gait analysts shows that there is ample difference between the observation of the gait features by the experienced experts as they made precise decisions in 71% of the cases. Studies also indicate that there is a difference in the capability and confidence of the qualified (competent/skilled/experienced/knowledgeable) and inexperienced gait analysis and cautions about the evidence submitted by the non-experienced gait analysts.
Irrespective of the limitations and criticism about the individuality and uniqueness and its admissibility in the court of law, forensic gait analysis may be considered as supporting/corroborative evidence for the identification of the criminals and perpetrators. Many forensic cases have been solved, and the criminals have been convicted based on forensic gait analysis throughout the world.
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