Solving Old Crimes with New Technology
Eurofins’ new DNA software heats up cold cases
The science of DNA profiling has advanced significantly over the last 20 years. The sensitivity and discriminating power of DNA tests means forensic scientists are now able to apply DNA technology in many situations that previously would have been unthinkable. However, the increased sensitivity of the technology can mean that many more ‘mixed DNA profiles’ are obtained. These are instances where DNA from more than one person is detected, which is common when body fluids have mixed or an object, a weapon for example, has had repeated contact from different individuals. In response to this challenge, Eurofins has developed its own proprietary software (LiRa) to assess DNA mixtures in serious crime cases.
Autosomal DNA profiling was first applied in criminal investigations in the UK in the late 1980s. As DNA profiling became more sensitive, the chances of detecting DNA from multiple individuals increased and so did the incidence of mixed DNA profiles. The interpretation of some of these profiles is straightforward, while others can be very complex. Eurofins has responded by developing LiRa, its own statistical software, to help courts and investigating teams to understand the strength of evidence in cases involving complex DNA profiles. The key output from the software is a likelihood ratio (hence the name LiRa), which is calculated based on two mutually exclusive propositions defined by the user – one representing the prosecution version of events and one the defence version of events.
Depending on environmental conditions and the quality of preservation of biological material, DNA can survive for many decades. This means, provided biological material has been retained and stored correctly, crimes that took place many years before the advent of DNA technology can be re-investigated. These crimes are referred to as ‘cold cases’ because they have remained unsolved despite the best efforts of investigators. Eurofins’ sophisticated software has been critical to helping solve several cold cases, including a 1984 violent sexual assault in Bradford, England, for which the assailant received a conviction 33 years after the attack occurred. Forensic scientists found a tiny speck of blood on a knife recovered from the crime scene and obtained a mixed and partial DNA profile from a swab of the area. The mixed and partial nature of the result meant that computing a weight of evidence for court was complicated statistically. However, using the LiRa software, it was calculated that the DNA evidence was 490 million times more likely to be attributed to the person of interest and an unknown individual as opposed to two unknown individuals.
The software was developed, tested, and is supported on an ongoing basis by Eurofins’ own in-house forensic software development team and statisticians.
The science behind
Initial DNA profiling techniques provided highly discriminating DNA profiles and compelling evidence of association, but also required several days, sometimes weeks, to produce a profile. They used radioactive probes and required a large amount of DNA (in forensic terms). Techniques have continued to evolve and become more sophisticated. Now, with the advent of PCR, DNA profiling has become super-sensitive. The old radioactive probes and Southern Blots have been replaced with fluorescent dyes and capillary electrophoresis (CE). Instead of X-ray film, DNA profiles are produced digitally and evaluated statistically, using specialist software that is costly to purchase.
