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CSI Foils Felons

Police are using sophisticated laser scanning techniques to create virtual reconstructions of crime scenes - helping detectives solve difficult cases and juries make more informed decisions.

Jimmy Lee Shreeve reports.

The hugely popular U.S. television show CSI: Crime Scene Investigation has often been slammed by real life police investigators for being too far fetched - stretching the facts as well as the science. In truth, investigating crime scenes is far from glamorous and involves a good deal of painstaking "plod" work. But it is getting decidedly hi-tech, especially in more complex cases.

One of the key technologies increasingly being used today by police is laser scanning, a technique that creates highly accurate 3-D reconstructions of crime scenes. These reconstructions can be viewed on large plasma computer monitors and can even be explored from different angles and points-of-view - much as you can in computer games.

All this is helping detectives crack cases and juries make more informed decisions. "Understanding evidence documented on a 2-D drawing of a staircase is difficult. (But) if you create a 3-D staircase and cut-away, the relevance is often clear," explains laser scanning expert Derry Long of Plowman Craven and Associates (PCA), a land surveying firm, which also numbers police authorities amongst its clients.

Long - who spent 12 years as a civilian employee of the Metropolitan Police - has set up the first hi-tech call-out team in Europe for criminal investigations. He and his colleagues are on call 24/7 and respond to growing numbers of incidents every year. Their job involves scanning the area where a crime has been committed and then recreating it down to sub-millimetre level using the digital data collected, along with standard photographic documentation and notes taken from the crime scene.

The kind of detail offered by 3-D laser scanning can make all the difference to solving the puzzling aspects of a crime. In one particular case, reported in the U.S. Government Technology magazine, a murder was thought to have occurred in a kitchen, but no one could work out how the body ended up in the hallway. By recreating the crime scene virtually, police were able to examine the area from different points-of-view and work out what happened. Thus gaining greater insight into crime.

Large scale

Laser scanning is also particularly useful when a crime has been committed outdoors. Not only does it speed up the mapping of very large crime scenes, it also enables the investigators to glean far more detail. When a political execution was committed in a large pasture in Ireland, investigators used laser scanning to create a virtual map of the scene and quickly gained vital information they wouldn't otherwise have got using traditional methods. In the past, the sheer size of the area would have been an issue and would have involved protracted surveying (using a theodolite), sketching and photographing.

"The beauty of laser scanning is it can capture enormous scenes down to the minutest level," says Mark Harrison, MBE, National Police Search Advisor and one of the officers involved in the investigation in Ireland. Harrison first used 3-D laser scanning in February 2002 when faced with finding possible victims after the Yarlswood detention centre for asylum seekers, in Bedfordshire, burnt down. It was the largest building-based crime scene in Europe.

"There was concern that bodies might have been in the burnt out building, so a forensic de-construction of the site had to be performed," he says. "My greatest difficulty was how to capture the massive crime scene. Because I have close ties with researchers in both universities and the private sector I was aware of laser scanning, which was just coming on to the scene."

Minimizing contamination

Another advantage of laser scanning is it minimises the possibility of crime scene contamination. "Contamination can take many forms," explains Harrison. "Someone might touch an object, leaving their fingerprints. Or they might inadvertently move or take evidence from the scene - possibly by picking up hairs on their shoes. The great thing about laser scanning is it is non-intrusive. It lets you capture a scene from a stand-off point-of-view, which greatly reduces the risk of contamination."

Harrison also points out that scanning a crime scene digitally before anyone enters is also a way of cementing that scene in stone. When a case comes to court this can make a big difference to a witness's recollection of events. "From an evidential perspective it's brilliant because you can pinpoint where everything was," continues Harrison. "It's also interactive. You can put a digital representation of a witness into the 3-D model and move them around the scene. This can help verify what they could or couldn't have seen. It might turn out, for example, that they couldn't have seen an incident as clearly as they thought they could because an item of street furniture was in their direct line of sight."

Laser scanning works equally well in documenting accident scenes. Although not involved personally, Harrison points out that the technology was used earlier this year by British police to re-examine the Paris tunnel where Princess Diana died in a 1997 car crash.

Risk of falsifying evidence

The virtual magic of 3-D laser scanning is also used to create the stunning visual effects in fantasy movies such as Tomb Raider and Harry Potter. For some, the fact that laser scanning technology is used by the entertainment industry to create highly believable, yet unreal worlds, triggers off alarm bells. "We've got to embrace these new techniques, but we must clearly understand that the digital world is an easy one to manipulate," warns Dr David McLay, OBE, of the Association of Forensic Physicians. "Not only that, but we must ensure that there is no intentional or even unintentional falsification of the crime scene and what can be deduced from it."

He also believes it is too easy to be seduced by the lure of new technology: "Looking at it from the point-of-view of jurisprudence, I would hope there is always somebody there to challenge this and bring people down to earth a little bit." Advocates of laser scanning agree that data, by its very nature, can be tampered with. But insist that what is important during a criminal investigation is preserving the chain of evidence.

"When laser scanning data is captured it is date stamped and strict protocols are put in place to ensure integrity and continuity of evidence," explains Tony Grissom of California-based Leica Geosystems, one of the leading manufacturers of laser scanning equipment. "While it is conceivable that data could be tampered with - intelligence agencies like MI5 or the CIA, for example, have the ability to do pretty much anything - it is an extremely unlikely scenario."

U.S. fragmentation

Although the main thrust of 3-D laser scanning product development has been in the U.S., the technique is more commonly used by police forces in Britain. According to Raymond E. Foster, a retired Los Angeles Police Department (LAPD) lieutenant and author of Police Technology (Prentice Hall 2004), the main reason for slow take up in the U.S. is fragmentation. Unlike the U.K., which has 44 police agencies answering to the home office, we have over 18,000 state and local police agencies answering to their city, county or state. Getting them on the same page when it comes to advances in technology is not easy," he says.

Looking back on his time in the LAPD, Foster can recall numerous incidents where 3-D laser scanning technology could have been used to good effect. "I can think of a ton of homicides where the ability to go back to the scene could have proved the key to cracking the case."

How does 3-D laser scanning work?

Three-dimensional laser scanning systems work by projecting a laser beam across an area. The laser light bounces off objects and returns to a digital sensor on the scanning device. Laser scanning essentially measures millions of points at a scene - referred to as the "point cloud." These are then converted into appropriate digital format and are used to virtually recreate the area that has been scanned. Any desktop or laptop computer can take the laser scanned data file and display the material as a 3-D image that can be explored, much like you can in a computer game.

About Jimmy Lee Shreeve

Jimmy Lee Shreeve is a writer and journalist living in Britain, but writing for newspapers and magazines around the world. He is author of a cult bestseller set around hoodoo, blues and rock and roll, published by St Martin's Press. And is currently writing a true crime title called "Blood Rites", which investigates the growing numbers of ritualistic murders, carried out by shamans and religious extremists, that have occurred in recent years in Africa, South America, and even in England, Ireland and the USA. Discover more at