Forensic Uses of 3D Printing
The use of physical models in court is nothing new. For decades now, small scale models of crime scenes or other pieces of evidence have been entered into court to show jurors where and how a crime may have been committed. However, the use of 3D printing for investigative or court purposes is still relatively new. This may be in part because of a perception of a complex technology, cost, or simply a lack of understanding of what can be done with 3D printing. It’s a wonder why more investigators, lawyers, and expert witnesses haven’t seen the benefit of 3D printing for use in court.
For anyone who has been following the trends in 3D printing, it comes as no surprise that there has been significant growth in this area in the past several years. New companies have formed providing small, at-home 3D printers for ready-made parts while larger and more professional printers allow for a variety of materials to be used with color, tight tolerances, and improved surface finishes. Materials and technologies range from powder based materials, liquid resins, metals, and ceramics. Traditionally, these 3D printing systems have been used by engineers to create new or replacement parts while hobbyists and artists have the ability to create ready-made pieces to their own specifications. However, in the case of the criminal investigator or forensic scientist, only a few have actually used this technology in court.
Perhaps the greatest reason for the 3D printing boom has to do with the availability of 3D digitizing systems such as laser scanners, structured light scanners, photogrammetry, and similar technologies. The cost of hardware has become affordable and the ease of use of photogrammetry software has made these technologies available to the average consumer. A quality laser scanning system for smaller parts can be purchased for less than a few thousand dollars and in the case of photogrammetry, there are several low cost and even freely available programs and services offered to create highly detailed 3D models of everyday objects.
3D printers are available in a wide range of prices from the high end at over $40,000 USD down to the low end where an off the shelf unit may come in for as little as $500 USD. Of course, accuracy plays an important part in the cost of a system as does the size of the object that can be printed. In addition, the type of material and technology used (e.g. thermoplastics, photopolymers, ceramics, or metal) will drive the cost of the 3D printing system. The most common materials are thermoplastics which are the best value for most types of applications. One need not purchase a 3D printer in order to get a part made. There are many service providers available with physical locations to order and pick up printed parts. Alternatively, there are online service providers that allow you to upload, optimize, and print custom 3D models that get delivered through the mail.
The first step to creating a 3D printed object is to be able to digitize the object into a 3D model. Although terrestrial laser scanners have seen some increased use in law enforcement agencies, close range scanners that accurately record smaller pieces of evidence like skulls, bones, and shoes are not commonly owned or used by police departments. This is one reason why 3D printing for forensic use is not such a common practice. Fortunately, a local service provider with equipment capable of digitizing a particular piece of evidence should not be too far away.
The second step after an object has been documented in 3D is to ensure that the model is made into a continuous volume without any “missing pieces”. 3D printing is a process of combining materials, one layer at a time, to make objects from 3D model data. This is opposite to a subtractive manufacturing method such as machining. The benefit is that 3D printing allows for very complex parts to be made that would be impossible with other manufacturing methods. However, much like stacking layers of blocks on top of each other, there must be at least a partial block underneath to support the next layer on top. Therefore, the 3D model usually requires some preparation to fill any gaps and “solidify” the object into a water tight mesh.
The final step is the actual printing process itself. Similar to a regular inkjet printer, there are different quality settings that can be chosen for most 3D printers that define the surface finish and step increment of the part. Depending on the shape and size of the part, print times can range from just a few minutes to several hours for more complex parts.
Now that the 3D printed model is made, what can be done with it? Applications include training aids, investigative tools, test pieces, or as evidence submitted in court such that jurors may physically hold a replica of an important object in their hands. Below are some further examples of practical applications for 3D printing in the forensics field.
Creating replicas of pieces of evidence is certainly not a new practice in forensics. For years now, investigators and scientists have used materials such as dental stone to create casts of footprints, Mikrosil for tool mark impressions, and other materials that can replicate the surface of an object either by impression transfer or curing. Although footprint casting with dental stone is a very common technique, it is not always practical when the substrate material is prone to deformation or when the substrate is rapidly deteriorating.
Time can often be a factor and in many remote areas where resources and equipment may not be readily available, first responders have an opportunity to capture photographs of evidence using nothing more than a digital camera. Utilizing advanced photogrammetry software such as PhotoModeler Scanner1 or 3DReality,2 a dense and accurate surface model can be created. Also, it is important to note that the 3D model is a replica of the footprint and not a surface that is cast as a “negative”.
Subsequently, the created digital model can be converted into a readily acceptable format for 3D printing and in the absence of more adequate casting materials, time, or resources, laser scanning or photogrammetry can prove to be of benefit. Figure 1 shows a 3D digital model of a footprint made in snow that has been developed with 3DReality. The model can be easily turned into a 3D print and utilized to make comparisons.
Facial Reconstruction and Identification
When skeletal remains are found and the skull is intact, it is possible to utilize the skull to obtain information about the type of person who was found. Gender and race are able to be determined from various landmarks on the skull to assist with identification of the individual.3 At the Central Identification Laboratory of the Joint POW/MIA Accounting Command (JPAC), they have a mission to identify the remains of American soldiers from past military conflicts. Among the lab’s tools for forensic identification are multicolor 3D printers. For example, JPAC prints a model of a skull using digital information from CT scans of the remains. The 3D printed skull is then photographed from multiple angles and superimposed with photographs of known soldiers to gauge potential matches, a process called “skull photographic superimposition.”4
Some mention should be made that these techniques need not be obtained from a CT scanner since photogrammetry or other 3D scanning systems are capable of capturing the data at different levels of detail depending on the need. Figure 2 shows a skull model created solely using photogrammetry. Photographs were taken from around the skull in small increments and, once processed, a highly detailed 3D model is created. This can subsequently be converted to a STL file format that is universally accepted across almost all 3D printing systems. (See Figure 3).
Fingerprint examination is another area where 3D printing may prove to be useful. Small scanning systems such as those created by FlashScan3D5 allow for a suspect’s fingerprints to be captured fully in 3D. Although fingerprints at crime scenes are traditionally captured through the use of powder and tape, they are eventually scanned or photographed as a high resolution image. The source of the prints (i.e. parts of the fingers and palms) are all curved and contain highly detailed ridges and pores. The resultant 3D model is able to capture all the ridge detail and can be used for investigative comparison purposes. (Figure 4).
While in court, a fingerprint examiner could use a large replica of a suspect’s fingerprint to make identifications and comparisons by color coding certain ridge features (such as islands, crossovers, and bifurcations) and matching them to a found print at a crime scene. Jurors benefit by being able to easily visualize the 3D replica and they have the benefit of haptic perception.
Fingerprints are a good example of where we take something small and create it at a much larger scale to bring out specific details which would normally not be easily visible by the naked eye. Fingerprint examiners in training benefit similarly from having the ability to easily visualize and “feel” what an enlarged 3D replica of a person’s finger looks like before making a flat print comparison.
An interesting application was suggested on an episode of CSI: NY, titled "Officer Blue," aired December 1, 2004. Although the practical application might have been a bit far-fetched, the main premise falls along the lines of a virtual procedure known as the Virtopsy, first introduced at the University of Bern, Switzerland.6
The story line is about the search for a sniper who shoots and kills a mounted NYPD officer responding to a scuffle in Central Park. The bullet passes through the officer and lodges in his horse. To determine the type and origin of the bullet, investigators need to examine it. However, removing the bullet is a surgical procedure that puts the horse's life in danger. As an interim step, the investigators borrow digital data of the bullet taken from a CT scan of the horse and use it to create a model of the bullet on a 3D printer.7
Of course, there are practical issues with replicating a highly detailed model of a bullet in 3D using this approach, but in theory, a similar method could be used on the internal skeletal components of a shooting victim which may be impossible to document without an invasive procedure. Small bone fragments, bullet, or pellet particles lodged in clothing or internally may all be disturbed as part of a traditional medical examination. Through the use of CT and MRI scanning, the relative positions of objects remain intact and without further disturbance. An example of a pelvis created through 3D printing is shown in Figure 5. The benefit to the investigator or pathologist is that the object is able to be inspected first hand and if created at a one to one scale, measurements, bullet trajectories, and other important data may be recovered.
There is a special need for techniques that allow pathologies to be presented clearly in the courtroom. For medical laymen such as judges, lawyers, and especially relatives of murder victims, the presentation of autopsy photographs can be disturbing, making findings difficult to present this way. From a juror’s perspective, being able to see such an object which is much more familiar than trying to interpret radiographs allows for a better spatial appreciation and understanding of injuries. Unlike volume renderings, 3D printed models offer real three-dimensionality as well as a haptic component, which make it easier for medical laymen to understand.8
Vehicle accidents represent an area where much is disputed and litigated on a regular basis. In some instances, the complexity of an accident or a failed component may require more than just photographs to do a proper investigation. As more police agencies adopt laser scanners in their workflow, it is possible to scan vehicles just as they are found at an accident scene to give a more accurate account of how vehicles may have been found in their final rest positions relative to one another or to some other object (See Figure 6). Insurance companies do not hold on to “write-offs” indefinitely and they are often destroyed not long after the incident; erasing any chance of further inspection and all evidence with it.
In the courtroom, an expert witness can physically hold a model of a crushed car and point out areas that were of importance. In this manner, physical 3D replicas can preserve some of the evidence for future viewing by a juror. Crush and extent of damage can be shown to a juror based on the physical replica and it is possible to take multiple models of vehicles and show the engagement between them by simply “fitting” the 3D replicas back in alignment with one another.
Structural and Industrial Accidents
Along the lines of accident reconstruction, there is often much attention and investigation into the cause and origin of structural and large scale industrial accidents. In the case where a large structural member has failed, Haag 3D has used laser scanners to document crane disasters. The failure and analysis of the 3D scan data can provide clues to how and where an important structural member may have failed. Further, being able to recreate the conditions of the failure using a scaled model is also possible.
In a recent case, Haag 3D was involved in a project involving the failure of a crane where the combination of wind plus other man-made effects caused a massive failure of the forward portion of the lattice boom. The crane and building were recreated using 3D printing and then subsequently placed in a wind tunnel to simulate the conditions and effects of wind. (See Figure 7).
In the past, these models would have been created by model makers spending significant hours to recreate exact replicas. Today, the most difficult components can be 3D printed and the large component assembly can be left to an engineer or model maker. There is also the added benefit that parts can have intricate details and be highly similar to the real world counterpart; thus making the scaled model highly representative of the real world counterpart. This in effect, increases the accuracy of the analysis.
Other forensic uses of 3D printing are extensive and are open to creativity. Some of these might include:
- Printing a scale model of the first floor in a home where a crime was committed.
- Recreating a physical copy of a weapon found at a crime scene.
- Displaying bullet trajectories through a 3D scanned article of clothing.
- Creating a model of a suspect’s dentition and showing how well a bite mark aligns.
- Printing a scaled model of a collapsed building due to a bombing.
- Creating test pieces of a piece of evidence that might be used in an experiment.
Although there are few cases where 3D printing has been adopted for investigative or court purposes, the ability to physically recreate a piece of evidence is an interesting approach. The range of objects can be as small as a fingerprint or can be an entire crime scene that is scaled down to just a few feet. As investigators and scientists start to see the benefit of replicating evidence, they will need to begin looking at digitizing technologies such as close range laser scanners, structured light scanners, and photogrammetry. Once these technologies have been adopted and more evidence is captured in 3D, there will very likely be many more cases where 3D printing will be applied.
1. http://www.photomodeler.com/products/scanner/default.html - EOS Systems Inc.
3. Skull reveals gender and race. 2013, Science Illustrated, 6, 14-14
4. http://cunicode.com/accelerating-forensics-with-3d-printing/ - Accelerating Forensics with 3D Printing
5. Flashscan 3d, Richardson, Texas, http://www.flashscan3d.com/
7. http://www.cadalyst.com/hardware/3d-printers/on-job-3d-printer-helps-solve-forensic-mystery-csiny-5092 - On the Job: 3D Printer Helps Solve Forensic Mystery on CSI:NY
8. Lars Chr. Ebert, Michael J. Thali, and Steffen Ross. 2011. Getting in touch--3D printing in forensic imaging. Forensic Science International (Online) 211, (1): e1-e6
Eugene Liscio is the owner of AI2-3D (www.ai2-3d.com) and is also the President of the International Association of Forensic and Security Metrology (IAFSM). He is involved in reconstructing crime and accident scenes through the use of laser scanning and photogrammetry. He teaches at the University of Toronto in the Forensic Sciences program where he is involved in research into 3D technologies and forensic applications.