The NIJ recently awarded CSAFE researchers a grant to explore how to improve the usefulness of current forensic shoeprint analysis methods. Most often, research in footwear examination looks at randomly acquired characteristics that individually identify a suspect. Through this grant, CSAFE researchers are approaching the problem differently.
The new CSAFE project asks the question: What does it actually mean to use a match as proof of identity without underlying data that provides an estimate of how rare the matching characteristics really are?
“This is not a very common way to think about the problem, but it’s essential if we want to do any sort of quantification and look at the meaning of the weight of evidence,” CSAFE lead investigator Dr. Susan Vanderplas explains.
Right now, examiners are not able to use a numerical quantification of the frequency of shoe population. Shoeprint examiners can use the phrase, “in my experience this is a very common model of shoe.” Instead, CSAFE researchers are developing techniques to assess random match probability, an estimate of the answer to the question: “what is the probability that a person other than the suspect, randomly selected from the population, would have this profile?”
Lead investigator Dr. Susan Vanderplas provides an illustration. “For example, if you’re in a college town in the middle of winter, many people are likely to be wearing Uggs. If an investigator knows that, using this method they would be able to say, for example, that 30% of the population has these shoes, and this size is worn by 20% of that population, so 6% of the population might have shoes that could have made this print. So the fact that you found shoes that could have left this print in one person’ closet doesn’t actually mean that much. Examiners can say Uggs are popular but that can’t say there’s one in every 3 people you pull of the street is going to have shoes exactly like this.”
Using population data in a courtroom allows forensic examiners to explain to a jury that the smaller that probability, the greater the likelihood that the two shoes came from the same person.
However, there is currently no publicly available data to describe the shoeprint population in a given area. Some sales data is accessible, but that doesn’t necessarily match what people are actually wearing. Sales data is only available from certain sources, which is problematic when people buy shoes online or during travel. As a result, sales data may not align with what people are actually wearing in the area.
CSAFE researchers are collecting this data by collaborating with Iowa State University Professor of Engineering Dr. Richard Stone to build a scanner that would be left outside, collecting images of shoes as people walk across. Researchers will then sort the shoes into categories, such as this is a sneaker this is a dress shoe. Or, researchers could identify if the shoe has patterns such as triangles or quadrilaterals.
Vanderplas and Stone, along with their research team have already built a prototype of the scanner. Over the course of the next year, researchers will utilize engineering principles to shrink the device, protect the privacy of individual, and design weather-proofing techniques.
Forensic consultant Lesley Hammer discusses more challenges facing the field of footwear examination in a CSAFE webinar. To learn more about other ways CSAFE is addressing these issues, visit our research page and review this CSAFE webinar.