Ketan Agarwal death case: What is gait analysis? | Explained
The story so far: A Pune court has extended the custody of Siya Goyal and Chetan Chaudhary, the two accused in the Ketan Agarwal murder case, till July 3, 2026. The court acknowledged investigators who said aspects of the investigation were ongoing, including a forensic investigation into Mr Chaudhary’s walk. According to media reports, police plan to compare his walking pattern with CCTV footage showing a hooded person near the crime scene at Lohagad Fort, arguing that the analysis could help determine whether the person in the footage is Mr Chaudhary.
What is gait analysis?
Gait analysis is the scientific study of how a person walks or runs. Walking (or running) is a complex activity in which the body requires constant coordination between muscles, bones and the nervous system. Gait analysis breaks down these activities to piece together how a particular person walks.
In clinical settings, this analysis can be used to understand why someone is in pain or how a particular medical condition is progressing. Athletes use it to figure out how to run faster.
Similarly, forensic gait analysis has been used to assess whether a person’s walking pattern (recorded live or seen on CCTV footage) is consistent with that of a known person. It is often used as the sole evidence and is usually thought to confirm Other evidence, such as DNA data and/or eyewitness accounts.
In most cases, experts use the analysis to identify abnormalities in an individual’s movement patterns. For example, sometimes a person’s back pain may be related to the way their foot hits the ground. Doctors also use gait analysis to manage symptoms and as part of post-stroke care in people with cerebral palsy and Parkinson’s disease.
In fact, at least in Parkinson’s disease, Alzheimer’s disease, Lewy body dementia and multiple sclerosis, research found that changes in gait may occur years before more obvious symptoms.
What is the gait cycle?
To understand how a person moves, experts start by looking at their gait cycle, which is the sequence of events from the moment a foot touches the ground until the same foot returns to the ground.
The cycle has two broad phases. In the stance phase, your foot is in contact with the ground and ends when the toes push off. During this phase, the body absorbs the shock of hitting the surface while supporting your entire body weight. During the swing phase, the foot is lifted off the ground but also moves towards it to move to the next step. The body’s focus during this time is to ensure that the toes do not drag on the ground as the foot is positioned to land.
During gait analysis, a person performs multiple gait cycles while experts use instruments to monitor steps per minute, step length, stride length, angles of the leg joints, ankle rotations, and the force of the foot striking the ground. Sometimes the tools are just a clinician’s eyes and a notepad, so they record different aspects of your movement as you walk back and forth.
Today, experts also videotape a person’s gait cycles and then analyze them with a computer, using sensors called pressure mats and force plates to track where your feet apply the most pressure, and wearable sensors worn on the person’s body to track their movements in a real-world environment, such as a crime scene or sports field.
How is forensic gait analysis different?
In forensic gait analysis, experts can use a person’s gait to identify them in a video, just as a fingerprint is used to determine whether a person touched a surface.
In the case of Ketan Agarwal’s death, the police said that they have a video of a person near the scene of the crime and this person could be Chetan Chaudhary, one of the suspects. But since the person in the video’s face is obscured by a hoodie, police hope to confirm whether it is indeed Mr Chaudhary using gait analysis, among other methods.
In such cases, experts such as podiatrists or human movement experts often compare two sets of videos: images that are investigated and images that show the suspect walking at a different location/time. They pay close attention to the rhythm of the steps, the angle of the feet, the way the arms swing, and distinctive movements such as a slight limp or an odd tilt of the head.
Experts might conclude, for example, that the person in both videos is the same if there is a certain outward rotation of the right knee and an unusually short stride.
What are the police doing in the Ketan Agarwal case?
The Indian Express quoted an unnamed senior police officer as saying investigators would dress Mr Chaudhary in his “original hooded outfit” and then “walk again at the same spot at Lohagad Fort”. The officer then added, “The new recorded walk will be compared with the CCTV footage recorded on June 18.”
Police will use “AI tools” to “analyze the similarity” and “help verify its existence,” according to the officer.
According to published studies, here investigators can separate the suspect’s gait from the CCTV footage on June 18 and, depending on the video quality, the movements of the hips, knees, ankles, shoulders, etc. can evaluate their relative movements and/or evaluate the silhouette.
Later, when the suspect is walked near the crime scene wearing the same clothes, his walk will be recorded and evaluated again. By doing this at the very location of interest, experts can reproduce the information. effects of factors such as camera angle, perspective, tilt and lighting.
Finally, experts can compare the gait between the original image and the new image to identify similarities; The unnamed police officer said that artificial intelligence (AI) tools will be used for this.
What are the challenges in gait analysis?
Researchers have already pointed out some pitfalls in this technique. An example: quality problems In CCTV footage. Another is that most published gait recognition systems calculate a similarity score or ranking. However, a high score only means that the movements are similar to each other according to some models; IT does not install The same person appears in both videos.
The act of asking someone to recreate a walk can also change gait. People often cannot accurately recreate an earlier gait. And if they know they’re being compared to CCTV footage, conscious or unconscious their speed, stride length, stance, arm swings, etc. replace it.
Researchers also called Larger studies measuring error rates in CCTV footage recorded in realistic conditions, including where AI models are used as part of crime investigations. These models can produce Misleading scores if the use case differs from typical use cases in the models’ training data.
There is also an ongoing debate about how unique a person’s gait may actually be and the ability of different tools to identify this uniqueness. For example, cameras that record at different frequencies (e.g. 30 Hz and 250 Hz), the latter will be better able to capture some movements occurring within 20 milliseconds, while the latter will have a frame delay of 33.3 milliseconds.
Depending on the gap between the crime and the investigation, experts may also need to take into account age, gender, height and leg length, and gait differences due to changes in body mass.
These are just some of the reasons why gait analysis alone should not be used as definitive evidence to identify a person. Forensic investigators often recommend interpreting gait analysis or comparison in conjunction with independent evidence such as location data, witness statements, DNA, fingerprints, and/or other forensic findings.
