3D Imaging and Printing Helps Piece Together Fragmented Evidence
Written by Dr. Amber J. Collings & Dr. Katherine Brown   

IN FORENSIC INVESTIGATIONS, it is not uncommon to come across fragmented evidence—be it glass, plastic, or any other material that has been subjected to some degree of force. These broken fragments are put through a physical fit test, where they are manually pieced together. If the pieces fit neatly together, then we can assume that those fragments originated from the same object. This may sound straightforward, but manually handling the fragments of evidence is not always that simple. This is especially true when confronted with burnt human remains.

This article appeared in the September-October 2020 issue of Evidence Technology Magazine.
You can view that full issue here.

Generally speaking, burnt bone is fragile and requires extremely careful handling to avoid any further damage. Additionally, some of the fragments can be extremely small and difficult to manipulate. Reconstruction by manually piecing the fragments together then becomes particularly challenging. What if there was a way to reliably test physical fit without needing to excessively handle the burnt bone fragments?

3D imaging and printing is becoming more widespread within the field of forensic anthropology, and virtual techniques could just be the answer here. Our research set out to test what was feasible in terms of 3D imaging and printing burnt bone fragments for the purpose of physical fit. Could 3D-printed bone fragment replicas be used to accurately perform a physical fit test? We tested this using two different 3D imaging techniques: micro-CT and structured light scanning.

Structured light scanning (SLS) is a 3D-imaging technique that uses the projection of visible light structures onto the surface of an object. Calculating the distortion of the light structures allows the built-in software to determine the surface shape of the object in question. Although it requires multiple scans for each bone fragment in order to ensure the whole surface is captured in enough detail to permit physical fit, the SLS technique has the advantage of being particularly quick and a relatively cheap setup compared with micro-CT. Micro-CT scanners are larger and more expensive, requiring dedicated lab space and specialist technical knowledge to operate. To image an object, the micro-CT scanner uses an X-ray beam to take multiple scans, presenting them in a stack of 2D X-ray images. This stack of images can then be reconstructed into a single 3D volume.

After 3D-imaging the same burnt bone fragments with both the SLS and the micro-CT scanner, the virtual models were 3D printed using a Prusa i3 desktop printer. This model of printer uses fused filament deposition technology. With this process, heated plastic filament is deposited in consecutive layers to build up the 3D model layer by layer.

Figure 1. This image, taken from the paper, shows an example of the 3D models created using SLS (red, left-hand side) and Micro-CT (blue, right-hand side). The models have been aligned to demonstrate how they would fit together. In A and D, the white arrows highlight the same features on both models; in F and G, the white arrows show how those features can be matched across the fracture line.

As was expected, due to the higher resolution, the 3D prints generated using the micro-CT scanned models were of higher quality with more fine details included (Figure 1, A and D). Nonetheless, both scanning methods recorded enough detail to allow certain features to be matched across the fractures (Figure 1, F and G). This meant that the fragments could be aligned, generating a suggested match. The actual physical fit of the printed fragments, however, was much more accurate (producing a closer fit) with the micro-CT model prints, leading us to conclude that micro-CT paired with fused filament deposition 3D printing is the preferred option for a physical fit confirmation.

So, yes, it seems that 3D-printed bone fragment replicas can be used to perform physical fit tests. Not only does this methodology mean excessive handling of fragile burnt bone fragments can be avoided when completing physical fit testing, but there are a number of other exciting advantages. First, any fragments that are especially small or with specific micro-scale details can be scaled up, isometrically. The 3D print can be made large enough to visualize the small details and easily handle without changing the geometry of the fragments. The opposite is also true: any particularly large or heavy fragments can be isometrically scaled down in size, generating 3D prints that are lightweight and more manageable to handle. Finally, this methodology opens up the potential for physical fit demonstration within the courtroom itself, allowing jury members to interact with evidence replicas where previously not possible. This can be done virtually and physically, allowing on-screen and hands-on visualization and manipulation. This increase in the impact of the evidence could prove to be a positive addition to a trial.

You can read the full paper here: https://www.sciencedirect.com/science/article/pii/S2665910720300633

About the Authors

Dr. Amber J. Collings is currently a lecturer in Forensic Science at Teesside University. Her research focuses on the integration of virtual anthropology 3D imaging and printing techniques with the criminal justice system.

Dr. Katherine Brown is a Principal Lecturer in Forensic Science at the University of Portsmouth. Brown’s research projects explore new methods of building a taphonomic profile, focusing on entomology and 3D technologies.

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