R does CSI: Using R to nail break-in suspects

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You've probably heard (or seen in TV shows) how the unique pattern of rifling in a gunbarrel generates forensic evidence: microscopic scoring on the bullets left at the scene of the crime can be linked to the shooter by matching the marks to the firearm. What you might not know is that the same technique can be applied to other crimes: for example, scoring on a screwdriver blade can leave identifying marks on a broken-into window frame, which can then be linked to a screwdriver-possessing burglary suspect.

With screwdrivers, the process is a little more complex: there's never an exact match between scoring on the screwdriver and the marks left behind, and the angle at which the screwdriver is used affects the marks as well. But at the JSM 2012 conference, Iowa State University R user Amy Hoeksema presented a method of measuring the “fingerprint” of marks on the screwdriver tip (as shown below), and then using a statistical model implemented in R to decide if it's a statistically significant match to marks found at the scene of the crime. 

 Surface striaie Chisel tip

You can find the details of Amy's method in her JSM poster, linked below (PDF). Using this method, she can not only determine whether the suspect's tool was used, but even at what angle it was used, within 5 degrees! Amy told me that this method hasn't yet been used to solve any crimes to date, but I'm sure CSI departments would welcome a new tool like this in their crime-fighting arsenal.

Amy Hoeksema: Statistical Comparison of Tool Marks in Forensics

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