Written by Dr. Amber J. Collings & Dr. Katherine
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.
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.
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
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.