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Graphic element Research > Growth > Research projects > Measurements & testing projects > Weighing the evidence
Graphic element Weighing the evidence
    26-07-2001
 

With EU support, the 11 members of the Nite-Crime network, comprising forensic science institutes, chemical analysis, and other research organisations, are developing sophisticated chemical analysis (mass spectrometry) techniques. These will enable the identification - with very high certainty - of a range of non-organic materials. The techniques will be disseminated to forensic and other research institutes to enable the build-up of validated databases. Precise identification of the original source of substances such as glass, bullets and paint is invaluable in forensic studies.

Suspect materials
 
Image
Material witness: glass particles for analysis, which are found on suspects and at crime scenes, are very small compared to a paper clip.
© Bundeskriminalamt, Wiesbaden, Germany.
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Determining the exact origin of materials found at the scene of a crime can result in the vital evidence needed to implicate a suspect. This is especially true as criminals have become more sophisticated and now take care not to leave any materials or traces of their presence at the scene of a crime which can link them through DNA testing. There are many more traditional and long-standing methods that are used to identify traces of inorganic materials, such as refractive index, which can establish that two glass samples originate from the same glass source. However, there is often room for uncertainty with these methods, which may be unacceptable in a court of law.

Other problems complicate the issue still further:

  • often there is only a very small quantity of sample available, which means there may be enough for just one analysis, or the number of repeat or corroboratory tests that can be made is very limited.
  • the financial resources available to the police for research purposes are increasingly limited, restricting the extent to which sophisticated analyses are used.

The network members are:

  • Institute of Food Research, Norwich, United Kingdom (co-ordinator);
  • Austrian Research Centres, Seibersdorf, Austria;
  • Bundeskriminalamt, Wiesbaden, Germany;
  • Forensic Science Service, Birmingham, United Kingdom;
  • Kriminal Technisches Zentrum, Vienna, Austria;
  • Netherlands Forensic Institute, Rijswijk, The Netherlands;
  • Curtin University of Technology, Perth, Western Australia;
  • Eidgenössische Technische Hochschule Zurich, Switzerland;
  • FBI Laboratory, Quantico VA, USA;
  • International Atomic Energy Agency, Seibersdorf, Austria;
  • US Customs Service, Springfield, USA.
 
Unprecedented accuracy
 

The mass spectrometer is a specialised weighing machine. It uses the difference in mass-to-charge ratio of ionised atoms or molecules to separate them from each other. These ions must first be created, then separated and measured. Developments in mass spectrometry now offer a range of techniques for determining the trace-element composition or isotopic ratios of inorganic materials. The key advance is the combination of laser ablation - to create the ions - with various separation methods such as quadrupole, time-of-flight, sector or multi-collector ICP-MS (inductively coupled plasma-mass spectrometry). Parallel developments in the technology use ultra-violet or excimer lasers to obtain lower wavelengths with a much higher accuracy than was previously possible.

"Most analytical labs are already using quadrupole ICP methods," explains the Nite-Crime co-ordinator Jurian Hoogewerff of the UK's Institute of Food Research, "but laser systems are expensive and the laser-ICP combination would only be available at a regional level." Using laser ablation is a very attractive option for forensic investigators because the amount of sample required for testing is very very small and, afterwards, the sample remains almost unaffected and intact.

Laser ablation ICP-MS analyses a wide range of elements in a sample, and can determine less than one part per billion of some elements. It is now possible to distinguish between, for example, two pieces of glass from two genuinely different glass sources. This is because, although both might have some physical properties in common, such as refractive index, they are quite different as the glass fragments were made with the same type of raw materials but from different geological sources.
The principle of laser ablation is that a laser beam hits a sample within a closed area, through which a stream of inert gas is passed - usually a mixture of argon and helium. Particles from the sample mix with the gas to form an aerosol and, in this way, the mixture is transported to the mass spectrometer where it is ionised and determined.

"Quadrupole systems are the most commonly used," according to Hoogewerff, "while time-of-flight systems are extremely fast and can be very effective for transient isotopic signals." The multi-collector systems offer extremely precise measurements of the natural isotope ratio; however, both systems are new and very costly. The exact choice of which method to use for a particular problem will depend on a number of factors, including the difficulty and importance to the case of the substance's identification, the cost and availability of the equipment, and the availability of the highly skilled staff necessary to operate the equipment.

 
   Relating techniques to crime scenes…
 

In a murder case where the police suspect that a body may have been moved from the scene of the crime to the burial place, they will need forensic assistance. An examination of the mineral debris on the body or clothes can reveal the unique signature of its chemical constituents. "Comparing the mineral breakdown of the fragments from the two sites can show conclusively whether the body has been in either or both places," explains John Watling of Curtin University, Perth, Australia. "Similar analysis of mineral deposits in car tyre tracks can be related to places where the car has been." The new technique is a real boost to the work of forensic scientists as it can give an unequivocal answer using extremely small samples.

Microscopic samples of lead or other metal particles from bullets (down to 0.03mm) can be identified and even pieced together from the fragments left in a victim's body. Then their chemical identity is determined to find or disprove a match with bullets from the weapons of those suspected of the crime.

 
…And to fraudulent schemes
 

Stefan Becker of the German Forensic Science Institute of the Bundeskriminalamt Wiesbaden, Germany recounts one example of a non-personal crime which was elucidated by the new technique. The Institute was approached by a major German pharmaceutical company which suspected that a batch of its immune human blood plasma was not German-made but, in fact, had been produced in China. The quality of this serum was so high that no difference could be detected from the authentic German plasma. Only by analysing the trace element composition of its glass container could the true origin be ascertained as Chinese-produced plasma.

 
Building databases
 

One of the main aims of Nite-Crime is to develop standard procedures. These validated methods and techniques can then be used to build up databases of the composition of those inorganic materials commonly found at crime scenes - glass, bullets and gunshot residues, car paint and others. "All substances used around the house," says Hoogewerff, "are based on raw materials from some sort of geological source - once we understand the trace element and isotope signatures of these materials they can be traced through the whole production process."

Because the techniques are so new, work is still needed to make them strictly comparable. Decisions are required on the optimum conditions for laser ablation, which must be standardised before reference identifications of materials can be recorded. For this reason, the Nite-Crime network will concentrate during its first year on setting these standards; later it will develop protocols for the materials most commonly implicated in crime scenes.

 
   Spreading the word
 

The network is planning to hold workshops, linked either to international forensic conferences, or at the laboratories of network members. Aimed at forensic scientists, the workshops will train participants in the use of the new techniques to identify relevant suspect material. All the members of the network believe that in time the new techniques will become better known and applied by more skilled operators. Competition will eventually bring the prices of the test equipment down.

Work is already under way in Australia to build a mobile spectrometer for use at a crime scene, significantly cutting both police and forensic officers' time. The new mass spectroscopy method will be to inorganic analysis what DNA testing has been to organic and human material - the key to identification with a high level of certainty, once it becomes more widely available.

 
Suspect materials
Unprecedented accuracy
Relating techniques to crime scenes…
…And to fraudulent schemes
Building databases
Spreading the word
   

Key data

A thematic network has been set up under the Growth Programme's measurement and testing generic activity to assist in the fight against fraud and crime.
The project is developing analysis techniques capable of identifying the source of minute fragments of inert materials. It will help to provide evidence to link an individual to a crime scene.

Projects

Nite-Crime - Natural Isotopes and Trace Elements in Criminalistics and Environmental Forensics (project no GTC-2000-28029).

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