From prints to prison: Forensic podiatry and gait analysis gain ground

INCREASINGLY, lower extremity experts are being called on to assist with crime scene investigations by analyzing footprints, shoe prints, and the gait patterns of shadowy figures on security videos. For members of this fledgling field, as Sherlock Holmes famously said, the game is afoot.

By Shalmali Pal

The in-person diagnosis of lower limb conditions, or assessing foot and gait mechanics, is second nature to lower extremity practitioners. But what happens if the assessment required involves a foot that isn’t actually in the exam room—say, a shoe print embedded in the mud under a window, a footprint left in blood on a kitchen floor, or closed-circuit television (CCTV) footage of an otherwise unidentifiable person walking away?

What kind of deductions could be made about the absentee owners of those shoes or feet, the way they walk, and—importantly—their potential level of involvement in a crime? That’s when forensic podiatry and gait analysis enter the scene.

The now-deceased Norman H. Gunn, DPM, of Canada is credited with introducing the concept of forensic podiatry in the early 1970s; about two decades later, an introductory article on the subject appeared in the Journal of the American Podiatric Medical Association.¹ The Bandon, OR-based American Society of Forensic Podiatry (ASFP) was established in 2003, and four years later, a forensic podiatry subcommittee was established by the Hollywood, FL-based International Association for Identification (IAI).

“The field of foot evidence is relatively new,” said John DiMaggio, DPM, ASFP, founder and president, and a retired podiatrist who has practiced in Arizona and Oregon. “Forensic podiatry can offer additional information when a case isn’t conclusive, based on anatomy, biomechanics, morphology, and pathology. We can offer more details about a person and his feet.”

ASFP currently has 25 practicing podiatrist members, along with 15 podiatry residents and 70 students, both in podiatry and in other disciplines (eg, anthropology, medical examiners), said DiMaggio, who is a coauthor of the second edition of Forensic Podiatry: Principles and Methods.²

LER spoke with DiMaggio and other experts in the field about what they do, how forensic podiatry and gait analysis work, and how lower extremity practitioners can become involved.

Footprints and footwear

Although TV shows and mainstream media outlets tend to use the terms synonymously, there is an important distinction between footprints and shoe prints.

“If you are looking to match a suspect to a shoe print, the foot examiner is the main person to go to,” explained Michael Nirenberg, DPM, founder of Friendly Footcare in Crown Point, IN, ASFP vice president, and a contributing author to the Forensic Podiatry textbook. “If you are looking to match a suspect to a potential footprint, then the forensic podiatrist is the right person for that. You need a knowledge of the foot to make that comparison.”

Footwear examination has become more prevalent in crime scene investigation in the last two decades, and that expertise is typically limited to outsoles, DiMaggio agreed.

“When I hear the word ‘footprint,’ I think of the foot and not the shoe, and that’s where the podiatric expertise lies. As a forensic podiatrist, I can still examine the outsole, looking for heel wear or wear under the ball of the foot, but I can also examine the upper of a shoe and see where the wearer has a bunion deformity. Looking only at the shoe’s outsole would not reveal that kind of information.”

One case that was a win for forensic podiatry was the overturned conviction of Ray Krone, of Phoenix, AZ, for the 1991 murder of a woman named Kim Ancona in a local bar. His initial 1992 conviction was based primarily on expert testimony that his teeth matched bite marks on Ancona’s breast and throat.³

When that conviction was overturned by a state court in 1996 because of legal technicalities, Krone was retried and found guilty once again, based on the bite marks but no other physical evidence. While Krone was in prison (10 years overall, with two years on death row), his attorneys began reworking the case to prove his innocence. That’s when DiMaggio got involved.

A shoe print estimated as coming from a men’s size 10 to 10.5 sneaker was found at the crime scene, but this piece of evidence was not included in initial court cases. DiMaggio was called in by the defense attorneys to evaluate that shoe print and to make a cast of Krone’s foot. He submitted a report verifying that Krone’s shoe size was an 11 to 11.5 and that his foot could not have fit into the shoe that left the incriminating print.

The forensic podiatry evidence was part of the overall package, including new DNA evidence, that ultimately led to the conviction of the real killer and brought about Krone’s release in 2002.³

“Was the information about Krone’s foot the deciding factor that got his conviction overturned? I wouldn’t say that,” DiMaggio said. “I think the foot analysis that I performed added to the weight of evidence.”

A high-tech field?

While technologies such as 3D scanning have made inroads in the clinic, they haven’t quite caught on in forensic podiatry. That may be because the field is quite small and quite new, DiMaggio noted.

But technology is part of its founders’ vision. Nirenberg proposed the use of a fiber-optic arthroscopic camera for examining the inside of a shoe.

“The insides of shoes and boots often contain wear patterns and impressions,” Nirenberg wrote in the Journal of Forensic Identification in 2008.⁴ “These wear marks contribute to individuality and aid in linking a given shoe or boot to a specific person’s foot.”

Such wear marks may appear on the shoe’s insole or the upper, often in the form of an imprint left by the wearer’s foot. The inside of the footwear may also contain materials (eg, soil or blood) that could help place a suspect at a crime scene, Nirenberg explained.

Traditional examination of the inside of footwear involved using a small dental mirror or cutting the footwear open—what Nirenberg called a “shoe autopsy.” To examine the inner shoe with an arthroscopic camera, he advised starting at the posterior aspect and working forward to the toebox, noting “the arthroscope will allow the relationship between the foot’s impression on the insole and on the toebox to be clearly seen.”

Nirenberg told LER that arthroscopic examination also allows for preservation of the footwear, along with a record of the exam process.

“You can see a lot more detail with the fiber-optic camera,” he said. “You also can record the exam process in case the jury wants to see the inside of the shoe before it’s disassembled. The jury can see how you examined the inside of the shoe and any impressions of the foot.”

Going by the gait

Gait analysis for forensic purposes is defined as “the analysis, comparison, and evaluation of human gait including the components and features of gait, to assist the process of identification or to answer any other legal question concerning gait,” according to Forensic Podiatry.²

“Gait analysis works with what we call ‘class characteristics.’ These are features that show consistency and compatibility, but are not unique,” explained Wesley Vernon, OBE, PhD, DPodM, coauthor of Forensic Podiatry and retired head of podiatry services at Sheffield Teaching Hospitals NHS Foundation Trust in England. “As such, gait analysis can be used with varying degrees of certainty to suggest how likely or unlikely it is that the unknown person captured on CCTV is the same [as a potential suspect].”

These class characteristics include elements with which all lower extremity practitioners are familiar—the gait cycle, including stance and swing phases; single- and double-support phases; and any deviations from a typical gait cycle because of functional anomalies and compensation from underlying pathologies.¹

In 2007, Peter K. Larsen, PhD, a researcher in the section of forensic pathology, department of forensic medicine, at the University of Copenhangen in Denmark, and colleagues published a checklist for forensic gait analysis in the Journal of Electronic Imaging.⁵ Lower extremity areas of interest for forensic gait analysis are:

• General: Long or short steps, stiff or relaxed, signs of pathology
• Feet/ankle joint: Outward rotation, inversion/eversion, degree of “push-off” at toe-off
• Knee: Varus/valgus, knee flexion during stance
• Hip/pelvis: Abduction/adduction, rotation, tilt

These elements are then paired with upper body assessments, such as positioning of the shoulder, neck, and head.

Larsen’s group applied this checklist to help solve a 2004 bank robbery in Noerager, Denmark. They analyzed CCTV footage of the perpetrator walking in and out of the bank and standing during the robbery. They started by evaluating the general characteristics of the person’s gait and then analyzing each of the joint rotations. They noted the person on the footage had a “stiff gait with ‘heavy’ feet; marked outward rotation in the foot and ankle joint; neutral varus/valgus knee; and very little pelvic rotation.”

Once a suspect was picked up by the police, the gait analysis of the perpetrator on the footage was deemed a positive match with another gait analysis of a suspect by Larsen’s group. The gait analysis was further bolstered by a posture analysis, leading Larsen’s group to conclude “the perpetrator and suspect might well be identical to each other, but we stressed that these methods did not constitute identification in terms of…DNA typing or fingerprinting.”

That is one of the crucial points to remember with forensic gait analysis: It’s a tool that can help increase the likelihood of pinpointing a suspect, but it cannot make a definitive identification or offer information beyond the limits of the lower extremities. For instance, when asked if gait analysis could be used to corroborate an eyewitness statement regarding a person seen fleeing a scene, potentially confirming or refuting that account, Vernon answered “yes,” but cautioned that the witness statement would have to include some description of the suspect’s gait.

“Forensic gait analysis utilizes our knowledge of gait and, as such, a forensic gait analyst would not report on height, weight, etc, with their opinions being restricted to areas that fall within their own particular expertise,” he wrote in an email.

Other researchers offered similar caveats. A 2016 paper in the Journal of Forensic Sciences noted that analysis of gait patterns from CCTV footage, paired with photogrammetry (the science of making measurements from photographs), were important but challenging forensic tools. By way of example, the authors tested the feasibility of 3D reconstructions for forensic gait analysis, and found considerable interobserver variability in data interpretation.⁶

Larsen’s group stressed that “in our work, we have both overt and covert recordings of the subject. There might be a potential problem in using overt recordings if the suspect consciously tries to modify the gait pattern during recording…at present, we do not find it possible to positively identify a perpetrator based on image analysis.”

Ultimately, forensic gait analysis data are only as good as the footage provided for that evaluation, the experts agreed. Larsen explained to LER in an email that the frequencies of oscillations during normal walking range up to 6 Hz, so the 12 Hz to 15 Hz frequency that modern CCTV units use should be more than sufficient to clearly capture even the quickest ambulator.

In a 2014 study in Science and Justice, Vernon and colleagues showed that CCTV frame rate, which can vary from 25 frames per second to one frame every four seconds, can affect the ability of even the most experienced practitioners to identify gait characteristics on that footage.

“Every effort should therefore be made to ensure that CCTV footage likely to be used in criminal proceedings is captured at as high a frame rate as possible,” they noted.⁷

Vernon acknowledged that new technologies, such as digital media, can be helpful for playing back an image at multiple speeds or looking at multiple images simultaneously on a single screen.

“Computer engineers are working on developing approaches that will do automatic gait analyses and comparisons, but these haven’t yet been developed to the point where they can be used in [forensic] practice,” he noted.

Data on what does and doesn’t work for forensic gait analysis can be used to inform where cameras are placed in public venues. Larsen’s group found most gait features can be examined using a frontal camera view and another in profile to record joint and segment angles in the sagittal plane. Some venues also have a camera positioned overhead to provide a transverse view of a perpetrator; this view can be helpful for assessing the degree of rotation of the feet and step length, but in general, is not as useful as the frontal view, Larsen said.

Vernon added that proper storage of high-resolution footage is always important to maintain the integrity of the evidence and support any related gait analysis.

On solid footing?

Where does forensic podiatry fit into the overall landscape of usable or permissible evidence for solving a crime? Ruth Morgan, DPhil, director of the University College London Centre for Forensic Sciences, specializes in trace evidence dynamics, or “understanding the behavior of trace evidence in different contexts and within different environments over space and time,” and the interpretation of evidence.⁸

“Footprint and gait analysis are most aligned with other pattern-based forms of evidence [like blood pattern analysis, for example],” Morgan told LER by email. “Our trace evidence dynamics work looks at trace evidence [particulates such as soils, gunshot residue, and other traces such as trace DNA] and how it transfers, persists, and is preserved under different environmental conditions.”

For instance, Morgan’s group authored a recent study in Forensic Science International that evaluated the generation of footwear marks in blood.⁹ They reported that “footwear tread effects were also dependent on blood type, but the type of flooring did not affect the appearance of the mark.”

“The study first looked at whether there was a difference in replicating a case scenario in which a blood mark was purported to have been made by a shoe making contact with a blood drop on the floor,” she explained. “We tested human and animal blood, and the results were not consistent when the other variables remained the same. In comparison, if the same blood type was used, the type of flooring material did not appear to affect the blood pattern.”

As with all evidence, data gleaned from forensic podiatry and gait analysis needs to fit into the big picture, Morgan added.

“Our interpretation of evidence work looks at the whole forensic science process—from crime scene, to laboratory analysis, to the interpretation of that evidence and its presentation as intelligence [to investigators] or as evidence [in court],” she said.

Forensic podiatry has a connection with the US Supreme Court, thanks to the Daubert standard.¹⁰ In his chapter in Forensic Podiatry,¹ Nirenberg wrote that the highest court in the land “explained in Daubert that evidence is admissible under [Federal Rules of Evidence 702: Testimony by Expert Witnesses] if ‘it rests on a reliable foundation and is relevant.’”

In a 2014 case in Mt. Morris, WI, Robert Kasun was found murdered in a hotel room.¹¹ Investigators arrested Travis L. Peterson, who was staying in the room next to Kasun’s, and he was charged with first-degree intentional homicide. At the crime scene, blood was found near the body, and chemical enhancement revealed a footprint. Nirenberg was asked for his expert opinion—could the bloody footprint have been made by Peterson?

Nirenberg’s forensic podiatry analysis and report showed commonality between Peterson’s foot and the footprint, including the shape of the toes. Nirenberg noted the bloody footprint exhibited a dark ridge on the second and third toes, which matched the morphology of Peterson’s actual foot. The pattern made the footprint unique to Peterson, according to Nirenberg.

The defense attorneys challenged the validity of the forensic podiatry findings, so a Daubert hearing was held to determine if the footprint analysis, and Nirenberg’s testimony, was admissible. The judge in the case green-lighted both, and Nirenberg testified at the Peterson trial. Peterson was found guilty and sentenced to life in prison.

“This was the first instance of forensic podiatry being the primary subject of a Daubert hearing,” Nirenberg wrote in a 2016 Journal of Forensic Sciences case report.¹² “The hearing resulted in the court ordering this evidence admissible. The expert’s testimony contributed to the suspect’s conviction. It’s a win for forensic podiatry, because that Daubert hearing showed that the evidence met the Supreme Court standards. In that sense, it’s an important step for validating forensic podiatry as a subspecialty.”

The case also highlights the fact that lower extremity professionals with an interest in the field cannot rely solely on their medical expertise—a knowledge of crime scene investigation tech­- niques, the criminal justice system, and the basics of forensic science are essential.

“Interpreting elements of the foot is not like DNA or a fingerprint in terms of how definitive it is,” DiMaggio noted. “It’s important that podiatrists understand how to interpret evidence within the context of the criminal justice system.”

To that end, the ASFP has plans to offer in-person seminars and webinars in the future.

“It’s important to have the forensics foundation, and understand how forensics do and don’t apply to issues of the foot that we as podiatrists are more accustomed to dealing with,” Nirenberg said.

In the meantime, podiatrists who would like to learn more can visit the resources library at ASFP, or consider courses given through the IAI, the American Academy of Forensic Sciences, or the American Board of Criminalistics. The New York College of Podiatric Medicine in New York City, Temple University School of Podiatric Medicine in Philadelphia, and Barry University School of Podiatric Medicine in Miami Shores, FL, also have set up forensic podiatry groups for their students.

“We have very good, dedicated DPM members,” DiMaggio noted. “It’s at the student level that we have to get people interested if we are going to grow this field.”

Shalmali Pal is a freelance writer based in Tucson, AZ.