Forensic gait analysis is the analysis, comparison and evaluation of features of gait to assist the investigation of crime. Gait was first used as evidence in 1839 in London, England, when Thomas Jackson, who had a bowed left leg and walked with a limp, was identified by a witness, George Cheney. “I know him by his walk,” Cheney testified (Nirenberg et al 2018).
Gait is the pattern of movement utilized during locomotion, key elements being its dynamic and repetitive nature, the term being widely and appropriately used to describe patterns of locomotion in both humans and other animals. As Levine et al (2012) point out ‘gait’ and ‘walking’ are often used interchangeably despite the fact that ‘gait’ describes the manner or style of walking, and not the process of walking. Gait is not synonymous with walking, and a person will have a pattern of gait for any method of locomotion including walking and running (Kirtley, 2006).
An introduction to gait analysis and its use in the forensic context
Gait analysis is the systematic study of human walking, using the eye and brain of experienced observers, augmented by instrumentation for measuring body movements, body mechanics and the activity of the muscles (Levine et al 2012). Since Aristotle’s work on gait analysis more than 2000 years ago (Peck et al 1937), it has become an established science used extensively in the diagnosis, treatment planning and evaluation of interventions in many areas of healthcare and rehabilitation, and widely used in sports science (Baker 2007). High impact peer reviewed journals and international conferences regularly publish and disseminate research and case studies on all aspects of gait analysis. While much of this research relies on complex laboratory equipment to measure kinematic and kinetic data, the majority of gait analysis in the clinical context is undertaken using simple direct observation without such equipment or even video. This is referred to as observational or visual gait analysis, which remains an important clinical tool (Mayer 2002). The skills required to undertake observational gait analysis are taught in a number of degree level courses related to biomechanics, gait analysis and healthcare. Levine et al 2012, describe observational or visual gait analysis as “in reality, the most complicated and versatile form of analysis available”, but go on to describe four serious limitations of this approach:
• its transitory nature, with no permanent record
• the inability of the eye to observe high-speed movement
• the inability to observe forces
• the dependency on the skill of the observer
The first two of these limitations are overcome by the use of video to record the gait, which can then be replayed as many times, and at whatever speed is required for the identification of features of gait (Mayer 2002; Levine et al 2012). The analysis can be further enhanced by the use of appropriate video analysis software (Borel et al 2011), the adoption of a systematic approach to both the observation and recording of features of gait, which has been the subject of much research and publication in the clinical context (Perry 1992; Lord et al 1998; Read et al 2003; Toro et al 2007a; Toro et al 2007b; Rathinam 2014; Gor-García-Fogeda et al 2016), and the use of appropriate terminology (Birch et al 2015).
Forensic gait analysis uses observational gait analysis based on video recordings to assist in the process of identification. While it has been long recognised that a person’s gait has features that can be recognised, the science of forensic gait analysis is a more recent development. The work of Cutting and Kozlowski in 1977 has been followed by numerous peer reviewed publications exploring the use of gait as a contributor to identification, including the work of Birch et al in 2013, which specifically considered forensic gait analysis as practiced when analysing CCTV footage (Cutting and Kozlowski 1977; Birch et al 2013). This practice is based on the identification of positions and movements during gait, not forces. It nevertheless remains dependent on the skill of the observer, and practitioners entering this area of work should ensure that they have the appropriate education, training, skill and experience (Levine et al 2012; Toro et al 2007b; Viehweger et al 2010).
Since the first presentation of forensic gait analysis evidence in court much effort has been invested in ensuring that forensic gait analysis practice conforms to the same standards as all other forensic science disciplines. Engagement with the Forensic Science Regulator, the Chartered Society of Forensic Sciences, the International Association for Identification and the College of Podiatry helps to ensure and enhance the quality assurance of forensic gait analysis. The Chartered Society of Forensic Sciences oversees forensic gait analysis competency testing and the associated register of practitioners.