British police forces are reviewing more than 450 unsolved crimes in a push to capitalise on dramatic advances in DNA forensic science. The advent of new ways to collect DNA from items at crime scenes, coupled with powerful analytical tools, has made it possible to obtain DNA profiles of suspects from undetected crimes or cold cases committed nearly 20 years ago, according to a Home Office spokeswoman. The operation has already identified 42 suspects.
The reviews focus on serious, often sexual offences and encompass at least 451 crimes committed between 1989 and 1995. Forensic scientists are returning to items of evidence stored at the time, from scraps of clothing to microscope slides holding just a few cells obtained from victims.
This week, scientists at the Forensic Science Service, which manages the police national DNA database, used the pioneering technique of familial searching to help convict James Lloyd, a shoe fetishist who pleaded guilty to six sexual assaults at Sheffield crown court.
The conviction came after scientists recovered DNA from a 20-year-old sperm sample held on a microscope slide. While the DNA did not match anyone on the DNA database, scientists searched again for similar DNA profiles and found a close match with his sister.
The high-profile success follows the first use of a new intelligence tool known as pendulum list searching (PLS) which led to the conviction last month of Duncan Turner for a sexual assault in Birmingham in August 2005. Scientists working on the case found a mixture of DNA from different people on a pair of sunglasses found at the crime scene. They used PLS to generate a list of theoretical DNA profiles that could make up the mix. Some 500 pairs of theoretical DNA fingerprints were entered into the database, and one matched Turner. The FSS ploughed a further ￡ 6m into research last year and more powerful and precise techniques are in the pipeline.
Part of the push to review cold cases of sexual assaults comes from the development of a technique called Fish, or Fluorescent In Situ Hybridisation, which allows forensic experts to identify and pluck just a few male cells from a swab of female cells taken from the victim. The technique identifies male cells by dyeing green only those carrying the male Y chromosome. Once they are stained, another new tool, laser microdissection, is used to cut them out and collect them, so a full profile can be obtained.
Jim Fraser, a forensic scientist who served as an expert witness in the case of Michael Stone, who was convicted of a double murder in Kent in 1996, said advances in DNA science had already led to suspects being identified beyond the grave and would continue to become more powerful. "The long arm of the law is getting considerably longer-there’s really no hiding place now," he said.
What is the function of PLS Illustrate the use of PLS by scientists.
According to Cathy Turner, a consultant forensic scientist at the FSS, the rapid advances in DNA technology have transformed the role of forensic scientists. "We’ve gone beyond corroborating allegations to using DNA and other techniques to provide fresh intelligence," she said. The swelling of the police national DNA database, which now holds profiles for 3.5m people, has in the last five years quadrupled the number of cases in which DNA is used. It provides police with some 3,000 matches to suspects every month. The national DNA database has been criticised by privacy groups, who fear the privatised database could potentially be misused, but for police forces it is an invaluable resource, said Dr. Fraser. "None of this evidence is infallible, irrefutable or unarguable. But it’s pretty much the best evidence that’ll ever be presented to the criminal justice system by some considerable way," he said.
