The Tell-Tale Steps
By Les Linder
By Les Linder
Each person moves in a unique way, making it possible to identify them by the style or manner in which they walk or run – and law enforcement around the world is beginning to take notice.
Forensic gait analysis was first admitted as evidence in London in July 2000 (<R v Saunders), says UK Consultant Podiatrist and Podiatric Surgeon Haydn Kelly, and has since been used in numerous cases, including the high profile UK night stalker serial rapist case.
Gait evidence was first used in Canada in
The jury accepted the evidence, convicting the defendant of first degree murder and sentencing him to life imprisonment. The BC Court of Appeal dismissed the defence appeal in 2012 and the Supreme Court of Canada denied leave to appeal in 2013.
The process of walking is a complicated activity which generally begins with the movement of the pelvis, says Kelly. Our arms move to help counterbalance the distribution of weight from side to side and maintain the head pointing in the direction of travel.
When an individual’s foot makes contact with the ground a force is generated which travels into the foot up through the leg, knee, hip and spine. How the body deals with those forces – biomechanics – affects how an individual moves.
The body movement is unique to each person and this “signature” of the walk can contribute to the forensic toolbox and the fight against crime, says Kelly.
“Gait analysis is the study of the movement of the way in which an individual walks through the various stages of the walking cycle,” says Kelly.
As a form of evidence during a police investigation, security camera video is examined and compared to the known (control) footage of an individual. In the majority of cases, tape of the unknown person is compared to video of a known individual, resulting in scientific evidence admissible in court.
“In some cases, officers are faced with many hours of CCTV footage that needs to be painstakingly trawled through,” explains Kelly. “If the suspect is known and if, to the trained eye, the suspect has an abnormal or unusual gait such as a detectable movement of the knee or foot, for example, then it is much easier to help identify an individual. This can save investigators an enormous amount of man hours.”
Kelly said gait analysis helps to identify people at a crime scene, verify alibis by proving a person’s presence, eliminates suspects, locates and tracks persons of interest and reduces the time needed to analyze video.
“It may be a qualitative analysis or a quantitative analysis that is carried out, or both, depending upon what footage is available,” says Kelly. “For example, a rear view of an individual caught on CCTV camera would be compared to rear view footage of a known individual.
“During the investigation process, the CCTV footage is the ‘unknown’ footage in terms of the scientific analysis of it. Investigating officers may capture and record the suspect from overt footage, custody footage or during a surveillance operation, which is the ‘known’ footage. Analysis is then performed for both the consistent and different features of gait. It is very much a tool of identification.
“The technique may also be useful in confirming the links between series of crimes – there have been a number of cases of this. Incident footage of the perpetrators was compared to the covert footage of suspects and it was determined that the same individuals were responsible for the chain of crimes.”
Certain features of gait can be observed when a person is walking or running, he notes. “If one is presented with footage of the same individual, then any distinguishing features of gait will be identifiable.”
Gait must not be seen as simply a “style” of walking, says Kelly. At the detailed level, it is a complicated process in which terms have to be simplified for evidential purposes and understanding in court, he notes.
“Because gait is so unique to all of us, it is much more than just a basic examination of “the way we walk” and much more than simply studying an image or a left and right profile of the known person.”
Gait is studied by comparing the various phases of an individual’s walking cycle from the assorted pieces of video presented during an investigation, says Kelly.
“During a person’s gait cycle, for example, we may consider at what point an individual’s left foot begin a forwards movement and, at the same time, what is the position of the other foot. Different biomechanical movements occur at different times during the walking process and we have to compare like with like.”
Video is better than still images in demonstrating and explaining a person’s gait, Kelly notes.
The length of time it takes to conduct a full gait analysis depends on the amount of video to be viewed and examined, adds Kelly. An initial view of one hour is often enough time to determine whether forensic gait analysis will assist an investigation.
“The quality of CCTV footage can sometimes be a limitation to this kind of forensic analysis,” says Kelly, “but the question which should be addressed is ‘what information can be derived from the footage’? There have been a number of cases where investigators considered forensic gait analysis late in the day, believing that video was of insufficient quality, but later recognized the use for it.
“As digital and real time footage become more ubiquitous and the awareness increases that forensic gait analysis is often of use where offences are captured on CCTV, this will be of increasing assistance to investigations.”
Another benefit of gait analysis is that complete head-to-head foot surveillance footage of an individual is not always required.
“Although a complete view of the individual in motion is preferable, it is not essential every time and is specific to each case,” notes Kelly. “We can proceed with limited footage of an individual as long as the same structures are seen”
ARMED ROBBERY IMAGES
CUTS: CCTV of Robber at jewellers Video footage of the suspect (right)
Forensic gait analysis was first used in 2000, says Kelly, when London’s Metropolitan Police Service Flying Squad contacted him for his help. A series of armed robberies had occurred across the south and south east of England and the force wanted Kelly to compare security camera video of the robberies and surveillance recordings of the suspects.
The analysis led to a successful prosecution and made officers aware that forensic gait analysis is a valuable tool for identifying perpetrators.
“The advice and subsequent evidence provided by Haydn Kelly was fascinating for us and the jury,” said DI Wilf Pickles at the time. “It was key evidence against a team of dangerous armed robbers… who were targeting high class jewellers in and around London and the Home Counties.”
There have been several cases of suspects admitting their guilt based on the visual forensic gait analysis evidence presented to them, Kelly adds, resulting in considerable savings on investigation and court costs.
Kelly sees a bright future for gait analysis both evidentially and for intelligence uses.
“With improving technology, databases and the appropriate support, this could become a facility as part of every police agency. We are already able to swiftly conduct gait comparisons. As technology becomes more readily available, as it already is in some countries, this will help analyzing electronic submissions very quickly.”
Savvy criminals who attempt to conceal their gait have no place to hide, Kelly notes. There have been cases where suspects have unsuccessfully attempted to hide or disguise their walk by wearing different clothing, for example.
Kelly has provided many forensic gait analysis opinions and reports which have been successful at trial. Forensic gait analysis has been used in hundred of cases and investigations worldwide, he adds.
Haydn Kelly has more than 20 years experience as a Consultant Podiatrist and Podiatric Surgeon and is an examiner for the Faculty of Forensic and Legal Medicine at the Royal College of Physicians, London. He is compiling the first textbook on forensic gait analysis and has written numerous medico-legal reports.