Inside out

Forensic clothing has become increasingly sophisticated to reduce the chances of crime scenes becoming contaminated, but a new study suggests the very act of putting on such a suit transfers traces of the wearer onto the outer layer and subsequently into the crime scene itself. Contamination is a somewhat dirty word in forensics, but, as technology makes it increasingly possible to gather results from ever smaller samples found at crimes scenes, it is an issue that needs to be constantly addressed. The benefits of using personal protective equipment (PPE) at crime scenes are well established. Whereas an officer entering a crime scene once did little more than put on a pair of gloves, they now wear a full hooded oversuit, shoe covers and face mask, as well as gloves. These outfits not only reduce the risk of any additional skin cells, hair or clothing fibres from the examining officer contaminating the scene, but also help protect the wearer from the risk of exposure to biological substances, dirt and liquid splashes. “There can be no element of doubt where scientific support is provided – continuity of evidence is the biggest challenge of modern-day policing,” said Roger Shearn, a former scientific support manager with the Metropolitan Police Service. “When selecting a protective coverall for gathering forensic evidence, a number of factors should be taken into consideration, the most important of which are the best possible protection of the scene and the best protection of the wearer.” The design, fit and comfort of PPE has evolved over the years, addressing and eliminating issues such as the ‘bellows’ effect, in which air trapped inside the suit – together with fibres and biological material – could be forced out through the sleeves when the wearer made certain movements, potentially contaminating the crime scene. Suits now have double-taped seams, are designed to be lint-free and offer full two-way protection. The suits are supplied in sealed bags and certified as being forensically ‘clean’ by the manufacturers, but a new study carried out by a team led by Dr Claire Gwinnett, Associate Professor in Forensic and Crime Science at Staffordshire University, and working in partnership with Staffordshire Police, has highlighted a potential new source of contamination. “While suits prevent contamination once inside, it doesn’t address issues of the wearer in everyday clothing, climbing into the suit at some convenient point near to the crime scene – and thus the potential for fibres and other trace evidence to be transferred from these clothes to the suit outer surface,” said Dr Gwinnett. “The issue is when we put the suit on. How strict are we when we take it out of the packet? Coupled with sweat and skin cells from the hands facilitating DNA contamination, the freshly-donned suit is a potential source of contamination waiting to be shed at the scene.” The study, details of which were presented at the Forensics Europe Expo 2017 at London’s Olympia earlier this month, focused on the transfer of fibres to the outside of PPE clothing. Participants were placed in a ‘minimum fibre environment’ and the suits checked to ensure they were as fibre-free as possible. The suits were then put on in the usual manner. Once fully dressed and at the point where they would be ready to enter a crime scene, they were subjected to a zonal tape lift. The experiment was carried out five times with each participant, wearing standard clothes for different times of the year, in different environments to represent both indoor and outdoor crime scenes, and also with clothes that shed fibres at differing rates. The study included both long-sleeved and short-sleeved clothing. The tapings were then examined and it was found that, on average, those wearing low-shed clothing had 225 fibres on the outside of their forensic suits; those wearing high-shed clothing had an average 437 fibres present. “It showed that a level of transfer was happening,” said Dr Gwinnett. “The question was, did it matter? Currently i