Feature

Laboratory Sleuths

Scientific evidence is providing police with a better chance of getting their man or woman.

By Vicki Hyde, NZSM

Forensic science has come a long way since the days of the detective's magnifying glass. Increasingly sophisticated techniques allow the police to catch criminals faster and to be more assured of their conviction.

Universities and research establishments are happy to be involved. They are able to gain much-needed income from hiring out equipment as varied as pollen databases and high-powered lasers.

The police have a long history of using scientific skills. The first forensic service assistance in New Zealand was provided by the Colonial Laboratory over a century ago. Since that time, chemists, physicists and botanists have examined all sorts of evidence -- bodies, bullets, fibres, firearms, pollen and paint.

Scientists from DSIR, universities and private organisations assist the police's Document Examination Section, Fingerprints Department and other sections dealing with evidence. They also provide guidelines for collection and handling of evidence. They can suggest new approaches in breath alcohol analysis or appropriate packaging for sending documentary evidence.

One recent article in the Police Bulletin noted that the document section can pick up indentations in notepads up to six layers below the original written material. It went on to remind police officers not to write their reports on top of such material.

Almost 15,000 blood samples are taken from suspected drunk drivers each year. These end up at the DSIR for testing, along with samples from the police and hospitals. The DSIR makes regular checks for accuracy in testing. They also maintain a second specimen of each sample for retesting by private analysts, if the defendant so requests.

Body tissue is also sent to the DSIR in cases where chemical analysis is considered necessary. Mass spectrometers and gas chromatographs are used to detect tiny quantities of drugs and poisons. This makes it easier for the coroner to determine the cause of death. Drugs are also tested to see if there are any impurities that might identify their source and means of manufacture.

Pollen

One of the smaller pieces of evidence that DSIR routinely examines is that of pollen. The Geology and Geophysics division in Lower Hutt has a comprehensive database on pollens occurring in New Zealand. The main emphasis is on fossil records, of interest to geologists for dating purposes. However, they also have a library of pollen data for plants currently found around the country.

"Pollen is everywhere -- in your hair, on your clothes, you breathe it in and out," explains the DSIR's Roger Cooper. Much in the way of pollen deposits are microscopic, making them difficult to avoid or remove.

By checking for pollen, DSIR scientists can establish where a person or object has or has not been. Samples are collected and analysed for the distinctive pollen types that come from each plant species.

Cooper recalls a case where deer antlers had been obtained illegally. Pollen samples showed that the defendant had not been in the area claimed. There was no pollen associated with that area. This provided supporting evidence for a conviction.

Bullets And Blood

Bullets and blood make up another common source of evidence. The science of ballistics has become increasingly precise. Physical, chemical and microscopic tests can show when a gun was fired and how close it was to the victim. Skin traces can also indicate if a suspect was the one holding the weapon.

Blood types and chemical information from other bodily fluids have been used for many years in forensics. In recent years, sophisticated techniques of DNA analysis have come into use.

Samples of blood or semen are analysed by taking the distinctive genetic information and producing a DNA "fingerprint". The fingerprint looks something like a supermarket barcode and is highly specific for each individual. They have been used to obtain convictions in rape and murder trials, although acceptance of the new technology has been slow.

"In sex or assault cases it makes it very hard for someone to deny that they were involved," says Dr Geoff Chambers of Victoria University's School of Biological Sciences. He is also quick to point out that the technique can conclusively exonerate the innocent.

Chambers is interested in looking at genetic differences between different races. Polynesian peoples, for example, tend to have less genetic variability than Europeans because of the smaller island populations and lesser migration. This means that police using DNA fingerprinting on Polynesian suspects have to be aware that it may not be as discriminatory, according to Chambers.

"It takes a while to learn how to use these new tools", he adds.

Dr Patricia Stapleton has been considering running a workshop for solicitors on DNA technology and the problems involved. She is the single employee of DNA Diagnostics, a testing firm set up by Auckland University and a private company. Family law practitioners have been using her services in parentage testing.

"You get a much more accurate answer than conventional testing and it gives a definite answer," she says. Children inherit half their genetic material from each parent. By comparing the genetic banding of the mother and child with the putative father, parentage can be determined or discarded.

DNA Diagnostics charges $1,125 (GST inc) for their services, though Stapleton hopes that increasing usage will help to bring the costs down. It takes seven days to check the parentage using a somewhat tedious procedure. It involves extracting DNA from a 5 ml blood sample, separating it, fragmenting it, binding a radioactive probe to it on gel and washing it and exposing it to film.

Stapleton looks forward to having an assistant take over some of the workload, but sees the company as an important source of funding for other genetic research.

Laser Fingerprints

Dr John Harvey, of Auckland University's Physics Department, is also pleased by the money his department has earned on leasing services to the police.

"The Police Department gets access to expensive equipment cheaply and the university gets extra funds to get equipment," he says.

Twice weekly the police arrive to use the university's high-powered lasers for fingerprint analysis. Biological materials, such as the sweat and oils of fingerprints, fluoresce under the laser light. The advantage of using the laser is that the examination is non-destructive. Conventional staining techniques destroy or damage the evidence. The test is also relatively quick, allowing a large amount of exhibits to be examined in a short amount of time.

Fingerprint analysis has also been aided with the recent installation of a very powerful computer-based matching system. The Automated Fingerprint Identification System can search through hundreds of thousands of records far faster than can be done manually. It looks at the tiny areas where fingerprint ridge lines end or split, and can match these from sets contained in the database within minutes.

Vicki Hyde is the editor of New Zealand Science Monthly.