Reliable documentation of evidence generally begins at the crime scene. Historically, this documentation has occurred through only a few means: photography, hand drawn sketches, and two-dimensional diagrams created using surveying equipment and mapping software. For the most part, these are fairly inexpensive, relatively low-tech options that do not require excessive training to complete them properly. Three-dimensional laser scanning, a type of geospatial technology, has the potential to become a powerful tool in the crime scene documentation tool kit. While three-dimensional laser scanning can produce beautiful images and take precise measurements, it can be expensive to buy equipment and it generally requires a certain level of expertise to be used correctly. If researchers can demonstrate that this method is superior to others and that judges and juries will accept its merits, it may be worth the investment.
NIJ-supported researchers at the University of Tennessee performed a cost-benefit analysis of the three most widely used methods of crime scene documentation to determine the value of three-dimensional laser scanners compared to traditional approaches. The data were examined to understand the strengths and drawbacks of three-dimensional visuals in comparison to other documentation methods. Researchers assessed which visual aids are the most informative, fair, and accurate by asking lay people and forensic professionals to interpret mock crime scenes. This was done to accurately approximate how a judge and jury might perceive this type of evidence.
The research team created mock indoor and outdoor crime scenes to compare the precision and reliability of traditional crime scene documentation methods versus three-dimensional laser-scanned representations. Researchers asked lay people and forensics professionals questions about the crime scene based on the documentation generated by each method to evaluate how well each method depicted the crime scene and the associated evidence. Estimates of accuracy (based on the number of correct observations of the evidence depicted in each image) were used to examine trends associated with crime scene interpretation based on the age, sex, and/or profession of the survey respondents, and respondents were also asked about their general feelings toward each documentation method (i.e., preference, trust).
The research indicated that:
- Three-dimensional videos were the preferred documentation and photographs were second.
- Two-dimensional diagrams and photos yielded the highest average accuracies.
- Three-dimensional scanning technology is not quite as accurate, and is more expensive and harder to train on.
Based on the cost-benefit analysis of the documentation methods (three-dimensional laser scanner, photography, two-dimensional topographic diagrams, and scene sketches):
- Hand-drawn sketches are the least expensive to produce ($0.79/minute), followed by photography ($126/minute), two-dimensional diagrams ($297/minute), and three-dimensional scanners ($852/minute).
- In terms of labor intensity, photography captures evidence most quickly (7 minutes), followed by hand-drawn sketches (66 minutes), three-dimensional scanners (81 minutes), and two-dimensional diagrams capture evidence most slowly (94 minutes to final product).
- The average cost of equipment was least expensive for hand-drawn sketches ($82), followed by photography ($882), two-dimensional diagrams ($28,000), and three-dimensional scanners ($69,000).
- The average training cost for hand-drawn sketches was the least expensive ($1,000), while the other three methods all cost around $2,500 for training.
Practice Implications and Limitations
The data from this study can be used to better inform the budgetary and training decisions for forensics teams regarding the acquisition and utilization of three-dimensional scanners. Further, the criminal justice community can utilize the data regarding the three-dimensional laser scanning in the courtroom to provide estimates of accuracy and reliability in crime scene reconstruction to judges and juries.
Three-dimensional scanner video was the preferred method of documentation. As one law enforcement officer who was interviewed in the study put it: “It also allows a ‘virtual’ return to the crime scene to reevaluate evidence.” But three-dimensional laser scanning comes with the most significant cost in terms of training and equipment. One of the interviewees stated that they preferred three-dimensional video “because it captures all parts of the crime scene at different angles, whereas the other methods do not. The three-dimensional method doesn't leave room for people to imagine or fill in what is originally missing because the whole scene is given.”
However, there are some caveats with the use of three-dimensional laser scanning in this study, namely:
- An explanation of three-dimensional laser technology was not given to the survey takers, so there is uncertainty as to whether the results can be transferred to what a jury might think since a jury would get an explanation of the technology.
- Three-dimensional scene fly-through videos were not paused (but can be paused in real life) so as not to confuse the comparison to photographs.
- Measurement data was not recorded with the three-dimensional technology, but it is known to be more accurate (up to 1mm) than a tape measure (up to ¼ inch).
While three-dimensional products were preferred, many survey respondents (taken to represent potential jurors) were more hesitant about the validity of the data and wondered how it could be manipulated so as to obfuscate the truth. As one survey respondent noted, “These data suggest that, without proper explanations of three-dimensional scan technology, the policies and procedures required to create a three-dimensional video, and an explanation of the verifiable accuracy of the data, a jury may not trust a three-dimensional video.”
About This Article
The work described in this article was supported by NIJ award number 2016-DN-BX-0177, awarded to The University of Tennessee. This article is based on the grantee report “Implications of Three-Dimensional Laser Scanned Images for the Criminal Justice System” (pdf, 70 pages), by Giovanna M. Vidoli, Ph.D., Joanne Devlin, and Jenna Watson, The University of Tennessee; Michael Kenyhercz, Department of POW/MIA Accounting Agency; and Jason Keller, Naval Criminal Investigative Service.