Contemporary New Zealand scientists
Forensic science
Collecting soil from the sole of a boot, image courtesy of ESR
Forensic science
The overall success rate in DNA matching in New Zealand is world leading, with more than 55 percent of all unsolved cases loaded to the crime sample databases linked to individuals and more than 33 percent linked to another crime.
ESR’s 2005 Annual Report.
Like other scientific disciplines, forensic science took a leap forward with the development of techniques to profile DNA. First performed by Sir Alec Jeffreys at the University of Leicester in England in 1984, DNA profiling was introduced in New Zealand in the late 1980s, and followed by techniques based on Polymerase Chain Reaction (PCR) that made it possible to analyse increasingly smaller samples in forensic casework. PCR takes advantage of the ability of DNA to replicate itself. It exponentially copies, or amplifies, specific parts of a DNA molecule, resulting in a solution that contains many thousands of identical copies of the original molecule.
In 1996, New Zealand became the second country in the world to set up a National DNA Databank, in a joint venture between the Institute of Environmental Science and Research (ESR) and the New Zealand Police. This new crime-fighting tool is a database of DNA profiles from blood or mouth swabs taken from convicted offenders and volunteers. They can then be matched against DNA profiles from unsolved crimes in an attempt to link individuals to the scene or the crime. In 2005, ESR processed nearly 24,000 forensic DNA samples and linked one individual to 14 different crimes through the DNA databank.
Invisible samples
A decade ago, a bloodstain the size of an old 50-cent coin was the minimum sample size required for successful DNA analysis. Today, a nose print against a glass surface can be enough to link a person to a crime scene, and ongoing improvements to DNA technology have meant that even a few cells left behind on door handles, weapons or any other item an offender has touched while committing a crime can deliver a specific DNA profile.
During 2006, ESR upgraded its forensic laboratories to meet the extremely stringent conditions required for the analysis of such trace evidence. Pressurised air conditioning systems and transition areas that separate the sample analysis processes from other work spaces limit the potential of contamination and allow for the use of an extremely sensitive method of DNA profiling known as Low Copy Number (LCN).
LCN began as a joint venture between John Buckelton from ESR and the UK Forensic Science Services. It uses increased numbers of PCR cycles compared to standard DNA profiling and is capable of detecting as little as one DNA molecule.
Grains of truth
When it comes to tracing the movements of a victim, a suspect, a vehicle or any other item used during a crime, pollen and soil samples can provide crucial clues. Microscopic analysis of pollen and the mineral content of soil are used to reconstruct whether a crime involved more than one location, but both pollen and soils also lend themselves to more precise DNA analysis.
Forensic palynology refers to the use of pollen and spore evidence in legal cases. Individual pollen grains are robust and often persist when other evidence is lost – and combined with a geographical survey of locations around New Zealand to determine pollen profiles, analysis of a forensic pollen sample can reveal when and where a crime took place. GNS forensic pollen scientist Dallas Mildenhall has helped police investigating the theft of Colin McCahon’s $1.25m Urewera Mural Triptych, and the method has been applied in a number of criminal cases, including the Kirsa Jensen murder and the sinking of the Rainbow Warrior.
Scientists at ESR, led by Jacqui Horswell, have also developed a technique for soil analysis that extracts DNA from the microbial communities living in the soil. The method examines variation found within a piece of genetic code common to all known bacteria and it is sensitive enough to show whether soil samples come from the same site – providing a ‘soil fingerprint’ of the specific location. Samples can be as small as a piece of dirt on the sole of a shoe or the thread of a tyre, or soil stains on clothing.
Macabre task
After death, the human body decays in a succession of stages, each of which is marked by different insects and microbial communities living on or around the corpse. Forensic entomologists and microbiologists use their understanding of the different organisms that colonise a body to help estimate the amount of time elapsed since death.
Pigs are the closest proxy to humans when it comes to studying the organisms that live off the carcass. Their skin and their organs are similar to humans. Together with scientists at the University of Auckland and Victoria University of Wellington, ESR scientists have used pig carcasses in various locations to study post-mortem decay and the timing and succession of insect colonisation and bacterial growth associated with a corpse.
By Veronika Meduna
Further reading and websites
Image courtesy of ESR
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