How Virtual Crime Scenes Work

A forensics laboratory here is using a sophisticated computer system to reproduce crime scenes, recreating everything from the path of a bullet to the movement of a corpse with startling realism.
Image courtesy Silicon Graphics, Inc.

Police investigators and forensics specialists face challenging conditions when examining a crime scene. Often, the site of a crime can only be preserved for a short time, particularly if it's in a public area. Investigators must gather as much information as quickly as possible while doing their best not to disturb the scene itself. Also, crime photographers have to shoot scenes from multiple angles while attempting to preserve a sense of scale to ensure the pictures are meaningful -- both to investigators and to a future courtroom.

Today, some police forces are using virtual reality technology to capture and recreate a crime scene digitally. Several companies have developed numerous methods investigators can use when at the scene of a crime. Some replicate crime scenes with computer graphics similar to what you might find in a virtual reality video game. Other systems assemble photographs into a 360-degree virtual environment just like the photographic walkthroughs you may have seen on hotel and real estate Web sites. Police forces around the world have discovered that, if used properly, virtual environments can help the investigation process from its earliest stages all the way to a courtroom conviction.


Proponents of virtual reality suggested a forensics application for virtual environments in the initial days of the VR media blitz. Back in the '90s, virtual reality was a buzzword found in everything from news reports to Saturday morning cartoons. But as the public discovered that the actual progress in VR technology wasn't quite as advanced as the media seemed to suggest, interest waned and VR became known as a fad. Fortunately, many researchers, developers and computer scientists continued to work in the field, laying the groundwork for useful applications of VR technology.

In this article, we'll look at the two most common approaches using VR technology in crime scene recreation, as well as its advantages and disadvantages. We'll also look at the different stages in an investigation where a virtual crime scene can come in handy.­


Virtual Crime Scene Graphics

Many VR rendering programs start with a two-dimensional set of blueprints or sketches like this one.

The first virtual crime scenes were created in computer models. Investigators took careful measurements at a crime scene, including the dimensions of the scene itself and the relationship between all the objects inside the scene. For example, at a murder scene in a house, an investigator measured the dimensions of the room, the position of the body and the location of any other related information, like weapons or blood. Often, investigators used laser distance meters or a total station (a surveyor's tool) to ensure accurate measurements. Crime photographers took pictures of the scene from multiple angles. After the initial crime scene investigation, the investigator returned to the police station.

At the station, a computer operator took the measurements gathered by the investigators and entered them into a computer program. The program then rendered a three-dimensional space using that information.


Some programs required human intervention to make the spaces accurate -- one particular approach required a programmer to adjust the height of a room manually. The programmer used a Computer Assisted Design (CAD) program to adjust the computer model, create furniture or insert the figure of a body. Some early programs also included a library of common objects, like file cabinets or desks, to make the process a little faster and, therefore, less expensive.

Time and money were the two biggest obstacles to making virtual crime scenes a useful tool. The early programs needed a highly skilled computer programmer or graphics designer to make the environments convincing enough to be useful and immersive -- in other words, they didn't give the viewer a sense of presence within the virtual scene. Police forces needed software that had a much less steep learning curve and automated as much of the process as possible.

Today, several software companies offer products that automatically build rooms based on either basic measurements or a two-dimensional room plan. Most of these programs also include extensive object and texture (overlay graphic) libraries, allowing the user to customize the virtual environment and make it as accurate a representation of the real crime scene as possible. Most of these programs can even include the flight path of a bullet (as previously determined by investigators using standard forensics techniques).

TV series like “Bones” often exaggerate what VR systems can do.
Photo courtesy

The advantage to the improved virtual environment is that once it's rendered, users can now view the scene from any angle, including from vantage points that are difficult to access in the real world. By looking at the scene from different perspectives, investigators have more information that can help them accurately determine the course of events at a crime scene. Some programs also allow a user to add in animations, allowing investigators to view their theories in action.

If the program supports video output like a head-mounted display, the user can experience a strong sense of immersion, which can help witnesses recall more details or allow investigators to check lines of sight.

But modern virtually rendered environments have disadvantages. The biggest disadvantage is the need for an employee who has enough technical savvy to work with the program -- even with programs that automatically build environments, a user often has to make adjustments. Another disadvantage is that virtual environments are rarely perfect copies of the real crime scene. As a result, investigators or witnesses may become distracted by the imperfect simulation and miss important details.

In the next section, we'll look at a different method of constructing a virtual crime scene.



Some crime scene photographers use laser-scaling devices like this one, which projects a pattern of dots that acts as a point of reference.
Photo courtesy NASA

Some photogrammetry systems use a special camera mounted on a tripod that can rotate the camera's view in 360 degrees. The camera takes a series of pictures and sends them to a computer that has proprietary software designed to combine the photos together to make a seamless photograph of the environment. Users can change the point of view for the photo, turning in any direction.

These photogrammerty systems are much more efficient than a human photographer snapping photos from every viable angle. However, since it's on a stationary tripod, the camera won't capture any areas in an environment where the view is obscured from the tripod's position. Investigators have to move the tripod and take another series of photos to capture that perspective.


In many ways, photogrammetry has significant advantages over creating a graphical representation of a crime scene. For one thing, you don't need to be a skilled programmer or graphics designer to use the hardware and software. The machinery and computer programs do all the work for you, creating comprehensive photos in a few minutes. Another advantage is that it's not just a representation of the crime scene -- it's a series of actual photographs. Viewers won't be distracted by an unrealistic object model or a poorly chosen texture.

But there are some distinct disadvantages. Unlike a virtual model of a crime scene, you can't view a room from any angle -- you can only look around from where the investigators set the tripod for the pictures. Unless the investigators put the tripod in multiple places within the same space, you're stuck viewing a room from one fixed point. Photographs also aren't very good at accurately showing the depth of a view -- objects may seem to be closer or farther away than they should be.

Some photogrammetry software packages are very affordable, but the hardware tends to be expensive. For some police departments, the expense is justified because the software doesn't require someone with special training to use it. Some programs even allow users to use a normal digital camera instead of a specialized photogrammetry device. These programs require the photographer to shoot the same scene from multiple angles, then use the computer software to identify identical points in each photo. The software can then create a three-dimensional model by triangulating the identical points in each photo. This solution is much more affordable, but is less comprehensive than advanced photogrammetry techniques and requires more man hours to use.

In the next section, we'll look at some applications for VR crime scene technology.



Why Use a Virtual Environment?

Police can use VR simulations of crime scenes to evaluate a witness’ line of sight. In this example, the witness’ point of view is partially obscure, which might mean his statement is unreliable.

Why are police departments investing thousands of dollars in this sort of technology in the first place? For years, investigators worked from sketches, photographs and scale models to solve crimes. Why bring virtual environments into the process?

The most important reason is that investigators can preserve a facsimile of the crime scene indefinitely. Some crime scenes are in areas that receive a lot of public traffic and can't be cordoned off for an extended length of time -- the crimes scene clean up crew must return the scene to its normal state. By creating a virtual copy of the scene, investigators can revisit it whenever they want without inconveniencing anyone.


The applications for virtual environments in crime investigations include:

  • Data visualization - investigators can visually represent data in a virtual environment in ways that are impractical or impossible in a real one. In a shooting case, for example, an investigator can enter in data about the bullet's trajectory and path and see it plotted within the virtual reality. This can help the investigator visualize the position of the attacker.
  • Hypothesis formation and testing - virtual environments provide an easy way for investigators to create and test theories. Investigators can examine ways a criminal might have entered or left a room or the pathway of a struggle. Some virtual-environment programs have additional animation software. With the right personnel at the computer, investigators can create entire scenarios of how the crime might have progressed.
  • Witness statements - virtual environments provide investigators a quick and easy way to check statements from witnesses, or even help witnesses remember a crime. An investigator can check to see if a witness's account is even possible. He can view the virtual crime scene from the point where the witness says he was standing to see if elements like the line of sight match up with the witness' account. In another application, an investigator might allow a witness to explore a virtual crime scene to see if it helps him remember any more details about the crime itself.
  • Briefings - when working with a team of investigators, a virtual environment helps team members coordinate and explore the crime scene together. The investigator controlling the point of view can lead a group analysis of the crime scene, soliciting theories and suggestions from his team without having to go off site to the actual scene of the crime.
  • Training - Preprogrammed scenarios are excellent training tools. Trainees can examine a virtual crime scene, formulate theories and collect evidence.
  • Evidence in court - investigators use virtual environments to take a jury on a virtual tour of a crime scene, effectively illustrating their perception of how the accused committed the crime. The tool makes it much easier for juries to understand the relationship between the crime, the evidence found at the scene and the probable sequence of events. Some lawyers and computer experts worry that a jury might be swayed by poorly created virtual environments and that it's possible that the prosecution could misrepresent the actual sequence of events.

As companies develop user-friendly applications, we'll likely see police use VR technology more often. Several forces have expressed interest in using the technology to explore cold cases, possibly leading to an arrest decades after the initial crime. Many others are already using the technology to share investigation results with officers from different forces.

To learn more about virtual crime scene investigation and related topics, check out the links on the next page.


Lots More Information

Related HowStuffWorks Articles

More Great Links

  • "Scene of Crime Reconstruction." Advanced Interface Group, School of Computer Science, The University of Manchester.
  • "Visitors to Experience "Virtual Monticello" at New Orleans Museum of Art Exhibition." NSF Press Release. April 4, 2003.
  • 3Sixty
  • Beier, K. "Virtual Reality: A Short Introduction." University of Michigan Virtual Reality Laboratory at the College of Engineering.
  • Carlson, Wayne. "A Critical History of Computer Graphics and Animation." The Ohio State University. 2003.
  • Davies, Nicholas, et al. "Virtual crime scene reconstruction with integrated animated characters." Proceedings 18th European Simulation Multiconference, 2004.
  • Geodetic Services, Inc. "The Basics of Photogrammetry."
  • Gibson, Simon and Howard, Toby. "Interactive Reconstruction of Virtual Environments from Photographs, with Application to Scene-of-Crime Analysis." Advanced Interfaces Group, University of Manchester.
  • Gibson, Simon, et al. "ICARUS: Interactive Calibration and Reconstruction from Image Sequences."
  • Howard, T.L.J., et al. "Virtual Environments for Scene of Crime Reconstruction and Analysis." Advanced Interfaces Group, Department of Computer Science, University of Manchester.
  • iWitness.
  • Morley, Steven. "Virtual reality crime scenes." Vedette. No. 184, January 2002.
  • Pimentel, Benjamin. "SGI tries its hands at forensics: Italian police using computer graphics for crime scene analysis." San Francisco Chronicle, online edition. Monday, May 16, 2005.
  • Spraggs, David. "Detectives and crime scene investigators are using 3D technology to bring crime scenes to life." Police: The Law Enforcement Magazine. November, 2004.
  • Sutton, Raul, et al. "Integration of virtual reality technology into the curriculum of forensic science courses using crime scene investigations." Centre of Excellence in Learning and Teaching, University of Wolverhampton. Learning and Teaching Projects 2004/2005.
  • Visual Statement