When forensic specialists receive human remains in criminal investigations, the bones are not always in the best condition. Whether exposed to the elements for an extended period of time or extensive trauma such as a fire, damaged and fragmented bones need to be placed back together to further the investigation. Putting the pieces together in the lab can help investigators put the pieces together in the field, including placing suspects at the scene or drawing links between scenes.
Fragmented evidence needs to undergo a physical fit analysis (PFA) to determine what fits together and what does not. Typically, forensic specialists manually glue bone fragments back together—however, that is not an easy task when dealing with extremely small fragments of bone, bone that may pose a biological risk, or bone that is just too fragile to handle. So, Katherine Brown, senior lecturer at the University of Portsmouth’s Institute of Criminal Justice Studies, has proposed a new 3D-based method in a study recently published in Forensic Science International: Reports.
The first-of-its-kind study used 3D imaging and 3D printing to reconstruct small burned bone fragments into both a virtual and physical replica a jury would be able to understand. The use of 3D technology is becoming increasingly common in not only forensic analysis but the criminal justice system as a whole. In March, for example, UK researchers designed an experiment to see if 3D-printed models of skull trauma helped jurors better understand the technical language of forensic experts. Now, Brown and her team have taken another step forward.
For their study, Brown and colleagues first compared two different 3D imaging techniques to see which would be best for 3D printing a model. Using a dry archaeological human femur that had been fractured into two pieces through the burning and cooling process, the scientists compared the imaging results of micro-computed tomography (μCT) and structed light scanning (SLS). As expected, the μCT models depicted the bone fragments in greater detail; however, both scanning methods recorded sufficient detail to allow for feature matching and fragment alignment in reconstruction and PFA.
The forensic team then used those imaging models to 3D print a replica. Again, both μCT and SLS models produced prints that were of sufficient quality, but μCT was the clear winner in terms of quality.
“For all fragment pairs, the μCT models offered a closer and more robust fit compared with the SLS models, as well as showing endosteum surface structures in greater detail, which was of value in feature matching and alignment across the fragments,” the authors wrote in the paper. “The 3D prints generated using SLS scanning are therefore sufficient for visualization and demonstration of a fit, but if wishing to conduct a robust non-destructive PFA, μCT modeling is preferable.”
The team used fused filament deposition (FFD) 3D printing, which is one of the most common forms of additive material printing. While it has lower resolution compared with both imaging techniques, it still retained an appropriate level of detail to complete a PFA. One drawback to FFD printers, the researchers noted, is the need for support structures during the printing process. Occasionally, removing these structures once printing is complete can leave a “rough surface” on the finished model.
“Overall, the techniques demonstrated by the study are of value in forensic investigation and evidence presentation within the courtroom,” Brown said.
Photo: Katherine Brown in her lab at University of Portsmouth. Credit: University of Portsmouth.