Police could soon have a new tool to help trace criminals as scientists have developed a way of recovering "invisible" footprints from crime scenes.
Marks not seen by the naked eye are often left at crime scenes but previous attempts to enhance them with chemicals and light have often destroyed them.
A team of researchers in Scotland have discovered a chemical formula to make light footprints left on clothing and flooring more visible. As well as providing the shoe size and brand, clear footprints can reveal "individual characteristics" of whoever made it.
Dr Kevin Farrugia, who works at the University of Abertay in Dundee, said he had modified recent techniques for enhancing fingerprints left on fabrics to develop the world's first detailed images of latent footwear marks.
"Footwear marks can be made in many contaminants, for instance blood, mud, urine and dust, and they can be left on all sorts of different fabrics, like cotton or denim, as well as on patterned and dark material, which makes them more difficult to see," Dr Farrugia said.
"They might be left on the body of a murder victim if the perpetrator kicked or stamped on them during an attack, or they might be made by traces of blood that the perpetrator picked up on their shoes and left on the carpet, or other types of flooring, before leaving the victim's house.
"When someone steps in wet blood though, the first few prints they leave will be a wet smudge, so no fine detail from the footwear sole can be recovered. However, as the marks fade and become less visible, the pattern on the sole of the shoe, by contrast, becomes much clearer and better defined.
"It's these prints - the ones that we can't actually see - that are the most useful at a crime scene, especially when it isn't possible to recover other types of evidence such as fingerprints and DNA, because they can tell you things like what size, and even what brand, of shoe the perpetrator was wearing when they committed the crime.
"More importantly, because everyone walks differently, the sole of their shoes will have acquired what we call random and individual characteristics that are specific to that shoe and person, which means, when the police have got a suspect, they can get their shoes, and if the shoes match, it can lead to a conviction."
Dr Farrugia's research was carried out at the University of Strathclyde under the supervision of Professor Niamh Nic Daeid. His research was funded by the Home Office Centre for Applied Science and Technology, the Engineering and Physical Sciences Research Council and the University of Strathclyde.