Australian Teacher Used Mathematics For Solving Long-Running Murder Mystery

Editorials News | Jun-19-2019

Australian Teacher Used Mathematics For Solving Long-Running Murder Mystery

An Australian teacher used mathematics to solve a cold case of 37 years and help put a killer behind bars in the United Kingdom. Professor David Balding used a specialized math system to determine up to a one in a billion people who killed two 17-year-old girls in Scotland in 1977.

Christine Eadie and Helen Scott left the World's End pub in Edinburgh, never to see them alive again. Christine's body was found lying just outside the Scottish capital on the sand dunes of Gosford Bay, while Helen was found in a field of corn. The local police underwent a monumental persecution and the news of the murders quickly spread internationally.

But 30 years passed before someone was charged for the murders of teenage friends. Forensic teams found small damaged strands of DNA from the clothing that was used to tie the girls' wrists.

This led to the genetic code of Angus Sinclair, who was already behind bars, convicted of the murder of Mary Gallacher, 17, and Catherine Reehill, 17. His trial for murder against Helen and Christine began in 2007, but DNA technology was not yet so advanced and, due to the lack of witnesses, the case was circumstantial.

The tests said that the DNA was probably Sinclair's, but the scientists were not 100 percent sure. He was not convicted, because with an inconclusive DNA, the prosecution did not have enough evidence.

Professor David Balding worked with the forensic team of the London Metropolitan Police as a scientist. 'DNA, now it's black and white. But it was not early, "Professor David Balding told The Age.

Professor Balding began his search to find more convincing evidence linking Sinclair to the crimes. Professor Balding specializes in mathematical computational genetics, which consists of writing mathematical models instead of extracting DNA in a laboratory.

This process helped translate the lab work into "real world" responses, and then allowed him to use mathematics to see how strong the evidence was against Sinclair. Despite Professor Balding's experience, he did a great job for him since the DNA had degraded badly during the nearly 40 years it had been stored.

The long strands of DNA had split into small sections, similar to a rope that has worn away over time. Another obstacle for the professor was that each sample contained DNA from four people, with three billion bits of DNA in each person.

Both the girls and Sinclair and his brother-in-law, who was accused of murdering the girls, had parts of their DNA in the sample. The probable degradation of DNA, contamination and experimental noise were factors in the mathematical model of Professor Balding. It was through his calculations that he could determine that Sinclair was, in fact, the murderer, with a certainty of a billion. The "overwhelming" result meant there was little or no chance that it was not Sinclair's DNA on the clothes. Professor Balding presented evidence in court in 2014 under a forensic cross-examination, and his results were maintained.

This evidence was instrumental in leading to Sinclair's conviction in 2014 for the murders of Helen and Christine, and he was sentenced to 37 years in prison.

By: Preeti Narula