DNA evidence will often form a crucial element in securing a conviction.
DNA as a linking tool
Spanning a period from March 1996 to April 1998, three unsolved cases - a burglary, an aggravated robbery, and a rape - were linked through DNA profiling. A suspect was identified by DNA profiling as the likely offender. This discovery led Police to re-investigate the suspect's movements at the time of the crimes. His method of operation also indicated that he was responsible for an additional four offences, including a serious assault and an attempted rape. In 1998, the suspect was arrested and charged with all seven offences. He pleaded guilty to all charges and was subsequently sentenced to preventative detention.
ESR's DNA work played a vital part in the police case in two ways:
- by linking the unsolved crimes together; and
- by identifying the offender.
DNA as an exclusionary tool : Operation Harvey
One of the most powerful applications of DNA profiling technology is as a means of eliminating potential suspects from a criminal enquiry. Operation Harvey, which culminated in the arrest and conviction of serial rapist Malcolm Rewa, is an excellent example of the use of DNA as an exclusionary tool.
DNA profiling conducted by ESR linked eight rape cases between the period of 30 December 1988 and 23 March 1996. A range of past profiling techniques were used as well as the current STR technique. Armed with this information and other information derived from Police files, Police constructed a criminal profile of the likely offender. Voluntary samples were taken from over 3,000 men who fell within the offender profile and this DNA was compared to the DNA evidence collected from the unsolved cases. All of these men were able to be excluded with the exception of Malcolm Rewa.
In 1998 Malcolm Rewa was sentenced to preventative detention with a minimum sentence of 22 years. As a direct result of the DNA profiling conducted by ESR, over 3,000 innocent men were excluded as suspects from the inquiry - and one of the most prolific serial rapists in New Zealand was identified and convicted.
Diverse uses of DNA in Police investigations
DNA profiling is used as a powerful and accurate forensic tool in many different ways by the New Zealand Police in over three thousand cases per year.
Post-mortem examination
DNA profiling can be used in post-mortem examination where identification of the deceased is difficult:
- incineration
- drowning
- complete or partial decomposition
It is used in cases where the more common methods of radiography and odontology are unsuitable, such as in the recent Boxing Day Tsunami disaster.
Distribution of Blood
DNA profiling is also highly useful for resolving the distribution of blood at a crime scene. It is also extremely useful for investigating crimes where more than one person has been killed or injured. By identifying the likely source of a blood stain at a crime scene, the investigation team can determine the location of people during the offence and track how individuals moved through the crime scene.
Prolonged abuse
Another instance where DNA profiling is of value to the Police is in investigating crimes such as prolonged abuse. A recent case using profiling results proved that physical abuse occurred at a dwelling over a long period of time. The result was achieved by positively identifying the source of minute bloodstains distributed throughout the crime scene as belonging to the victims.
Historic cases
One of the most important and valuable qualities of DNA profiling is its ability to solve historic cases. DNA technology allows for samples from historic crimes that were never solved to be analysed. This has often led to the arrest of a suspect many years after the offence was committed. An offender was recently identified in the unsolved intruder rape of an elderly woman in 1988. This result was achieved through DNA profiling of samples collected at the time of the offence, which were unsuitable for analysis by the techniques of that time.
For further DNA success, click through to Success Stories.