Gait analysis explained: How the way you walk can point to your role in crime

AMONG THE evidence relied upon by a special court in Mumbai while giving the death sentence to a 44-year-old man for the rape and murder of a woman in the Saki Naka area of ​​the city, is a “gait analysis” report.

The prosecution relied on a forensic report comparing images from CCTV camera footage with a sample video of the way the accused walks, to corroborate his identity. This is the first time in Maharashtra that the test has been relied on by a court in a criminal trial.

What is gait analysis?

Gait is defined as a manner of walking or moving on foot. Gait analysis is a technique in podiatry medical care and the treatment of the foot, which is used to evaluate and diagnose conditions that affect walking and posture.

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The analysis can help experts zero in on the source of an injury or pain that determines the way in which an individual stands or walks. It can also be used by physiotherapists for treatment, and in athletics training so that athletes can perform better and in greater comfort.

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Gait analysis techniques have now been borrowed by forensic sciences experts to identify suspects in criminal cases. With footage from CCTV cameras becoming a crucial element in fighting and preventing a range of crimes especially in the cities, gait analysis has begun to be used as a tool for focusing on or eliminating individuals from a list of suspects.

So what exactly do gait analysts do?

For the analysis, experts compare the gait of a person seen in CCTV footage from the crime spot with a sample of the suspect’s walk. Using computer software, the two images are compared.

Forensic experts take various factors into account while making the comparison, including the movement of the feet and hands, the length of the stride, as well as the full gait cycle — from the time one foot touches the ground to when it touches the ground again after a step has been taken.

The software allows the expert to watch the videos in slow motion, and places them next to each other, frame by frame, for a comparison.

The analysis requires the sample video to be shot with the same conditions as the CCTV footage, including the same light conditions, with the person walking the same distance, and shot with the same camera angle.

The report of the expert can be used during a trial for corroboration of the identity of a suspect.

What happened in the Saki Naka rape-murder case?

The 31st witness in the Saki Naka case trial was a scientific officer from the state Forensic Sciences Laboratory in Kalina, who conducted a gait analysis based on CCTV footage from the spot and a sample video taken of the accused Mohan Chauhan after his arrest.

The officer submitted that gait analysis is a process by which the gait of a person, that is the “walking manner”, is compared with footage from a CCTV camera where a suspect is seen walking. The officer told the court that the hairline, forehead, and shoulders “were found similar” to that of the male person in the reference photographs (which showed the accused).

“Body structure and walking style of the person appears to be similar with the body structure and walking style of the person in the files,” the officer said.

The officer also flagged certain things that could not be compared: “The comparative features of the male person found in video file could not be extracted due to night vision, distance and height of camera. However, outline of head, shoulder were found similar to the person marked in the other video files,” the testimony said.

In its judgment passed on May 30, the special court relied on the gait test, stating that the accused’s identification from CCTV footage is corroborated by the deposition of the expert who conducted the gait analysis.

“PW 31, an expert in her evidence elaborately explained what is meant by gait test, how they compare the movement of the suspect and the sample video. In her evidence, she made it clear that they can compare the photographs and the clothes also with the help of images in the CCTV. They compared the clothes on the basis of its colour, pattern, size,” special judge HC Shende said.

The court added that nothing was elicited from the cross-examination of witnesses related to the gait analysis by the defense lawyer and that their deposition could not be discarded.

Chauhan was killed to death on June 2.

Is gait analysis a widely used legal technique?

The first widely known case in which gait analysis was admitted as evidence was in a criminal trial in London in 2000 against a man accused of carrying out a series of burglaries. The forensic expert, consultant podiatrist Haydn Kelly, said that the “walking mechanics” of the suspect resembled that of less than five per cent of the British population’s.

Criminologists and crime fighters in the United Kingdom, United States, and Japan are working to improve and fine-tune the technology for gait recognition. In China and Japan, the technology has been in use over the past few years as a surveillance tool, which, using artificial intelligence helps in the identification of individuals from their manner of walking in situations where facial recognition is not possible, such as in large crowds.

Has it been used in India earlier?

In India, police have relied on the gait test in a few other cases previously. An expert said that it was a recent addition to forensic sciences in India, and that the field was still developing.

* The National Investigation Agency (NIA) conducted the test on dismissed police officer Sachin Waze in its investigation in the Antilia terror scare case last year. CCTV camera footage near Antilia, the residence of industrialist Mukesh Ambani, showed a person wearing a loose kurta near the vehicle in which the gelatin sticks were planted. The person’s face was not visible. The NIA made a sample video of Waze and gave it for forensic analysis through the gait test for comparison.

* The gait test was also used in a murder case in Tamil Nadu last year.

* It was used to establish the identity of the assailants of journalist Gauri Lankesh in Bengaluru in 2017.

* It was also used in a rape case in Surat in 2018, where the investigators said that the analysis

enabled them to compare the walking style, body movements and other factors.

How reliable is a gait test in identifying suspects?

The degree of uniqueness of a person’s gait compared with other, more precise parameters used to establish identity, such as fingerprints or a DNA test, is yet to be established.

However, experts are using it as corroborative evidence, and to try to whittle down lists of suspects. Efforts are underway to reduce errors in gait analysis by considering various factors including length of the stride, height of the person, and the movement of the hands.

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