It's a given that criminals such as arsonists and serial murderers often return to the scene of the crime -- sometimes to relive the crime. But not only criminals do so.

Detectives, prosecutors and juries must also revisit the crime scene. Detectives may need to re-examine the evidence, prosecutors may return for case preparation and jury members may need to review the crime scene to make a decision.

To do their re-evaluations, investigators typically rely on photographic evidence and two-dimensional drawings. Since we live in a three-dimensional world, however, it can be difficult to visualize the positional relationships of evidence with two-dimensional tools.

What if agents could measure with extreme accuracy thousands of data points per second in a crime scene? What if an agent could capture that information, recall it and create his or her own virtual representation for use during a trial?

Through a combination of laser and computer technology, high-definition surveying (HDS) creates a virtual crime scene that allows investigators to maneuver every piece of evidence.

HDS reflects a laser light off of objects in the crime scene and back to a digital sensor, creating three-dimensional spatial coordinates that are calculated and stored using algebraic equations, said Tony Grissim, homeland security and law enforcement liaison for Leica Geosystems HDS, based in San Ramon, Calif.

"An HDS device projects light in the form of a laser in a 360 degree horizontal circumference," he said "The HDS is measuring millions of points, creating a 'point cloud.'"

Think of letting off an insect bomb in your apartment -- millions of particles create a fog, and the resulting cloud settles on all objects in your apartment. With HDS, instead of millions of data particles settling on the objects, those data points are bounced back to the receiver, collected, converted and used to create a virtual image of any location.

An average desktop personal computer can now take the data file and project that site onto your screen. Not only has the scene been preserved exactly, but the perspective can also be manipulated. For instance, if the crime scene were the front room of an apartment, the three-dimensional image allows the investigator to move around and examine different points of view.

Or perhaps the victim was found seated. An investigator could see and show a jury what the victim might have seen. If witnesses outside said they looked in a living room window, an investigator could zoom around and view what the witnesses could or could not have seen through that window.

Cloud of Information

"Understanding evidence documented on a 2-D drawing of a staircase is difficult," said Derry Long of Plowman Craven & Associates (PCA), a land surveying company based in the United Kingdom. "If you create a 3-D staircase and cut-away, the relevance of evidence is often clear."

Long spent 12 years as a civilian employee of Scotland Yard, where he designed police stations and developed computer modeling. At PCA, he uses HDS to re-create crime scenes down to the submillimeter level. Although PCA's focus is working with builders and developers, Long created the first HDS call-out team in Europe for criminal investigations.

His team, on-call 365 days a year, responds to about 150 incidents each year.

Many times, Long responds to a scene weeks after crime-scene investigations are concluded. His job, then, is to scan the scene, and then use the photographic documentation and crime-scene notes to re-create the scene.

Long recalled a recent homicide where the murder was thought to have occurred in the kitchen, but no one could determine how the body ended up in a hallway. By re-creating and studying the crime scene, investigators examined different points of view and the positional relationships of the evidence.

Lt. Raymond E. Foster  |  Contributing Writer