Expert Witness (20 page)

W
ho'd want a job where you have to stick your hand in the smelly shoes of people you don't know? Who'd have a job where you have to put your own feet into the same shoes? Forensic footwear examiners, that's who. At least we wear gloves and put plastic bags on our feet before we do either of those things, but you can't escape the smell from a pair of shoes that have been in a bag for a year since they were spattered with bodily fluids of varying colours and consistencies; no amount of biohazard labels stops the stench.

Footwear marks are not to be confused with footprints. Footprints are the marks deposited when someone's bare, or partially bare, foot has contact with a depositional surface. Footprints are the feet equivalent of finger prints; they are made of skin, are unique to individual people, develop in the womb just like finger prints and are treated in the same way as finger prints in the way they are collected from crime scenes, off objects and from suspects. Footprints are relatively uncommon, whereas finger prints are one of the most common methods of identifying ‘persons of interest'.

Footwear marks or impressions, on the other hand, pop up in casework all the time, particularly in burglaries. They are
also a sad legacy of serious assaults involving someone being on the receiving end of, literally, a good kicking.

So how do footwear cases work? Easy. Pattern matching. Footwear, such as shoes, boots, jandals/flip flops (depending on where you live), stilettos or whatever people wear on their feet, all have patterns on the soles. Soles leave patterns on surfaces. Match the pattern on a surface with the sole of a shoe — tie a suspect to a crime scene. In theory, it's simple. So how many cases have conclusive matches between the shoes seized from a suspect and patterns recovered from a crime scene? Well, that's some thing else entirely.

Obtaining a decent footwear mark from a crime scene is partly luck at the time the mark was deposited, partly skill on behalf of the crime scene examiner. Paper is pretty good for recording marks, so if you identify a possible entry point in your house (such as a loose window latch), put nice, clean white paper on the surfaces under the window so that if an intruder does get in, they'll land on the paper and leave a nice mark or two. Try to ensure the paper is on a firm surface — carpet is soft and the mark might distort. Kitchen lino can be pretty good for recording marks but you might not be able to see them with the naked eye, in which case the crime scene people will come along and enhance the marks with special techniques designed to maximise the detail.

Deep shag pile carpet is generally terrible for recording marks — too much flexibility and movement in the fibres. Best case scenario from long pile carpet is usually a vague indication of the size of the footwear mark, perhaps some idea of sole pattern, but not much else.

Footwear marks and impressions made in soil or mud
normally contain less fine detail than marks left on paper. Impressed marks, on the other hand, such as those made on a soft surface like damp mud, may record information about the depth of tread on a shoe, which is the sort of detail that can't usually be determined from a footwear mark on a flat, unyielding surface.

Footwear impressions in soil or similar material can be ‘cast' using plaster of Paris or some thing similar, just as dentists do when taking an impression of someone's teeth. The soil off the casts can be used for all sorts of useful purposes, such as pollen, soil and mineral analysis.

There are of course several factors to take into account when trying to interpret footwear marks recovered from crime scenes and comparing them with shoes from a suspect. When shoes are new or unworn the sole patterns are usually the same on all the shoes that were produced using the same mould. Shoes with the same sole patterns share what is termed the same ‘class characteristics' — they're not unique or individual so you'd be hard pressed to distinguish one set of brand new shoes from another, except if there's a little air bubble caught when molten material is poured into the mould.

I have seen several cases where air bubbles were visible on the sole of a shoe and in a mark from a crime scene. When combined with other information about the pattern on the shoe's sole, it has resulted in a conclusive link between a shoe and a crime scene mark.

When items of footwear are used, the soles become worn and after even a short period of time may exhibit various cuts and other damage features which are likely to be unique to that particular item. These are termed ‘individualising
characteristics' and can be used to conclusively link a shoe with a particular crime scene mark. Think of when you buy a nice new pair of shoes and after your first walk down the street, the soles are scratched, whether you're wearing Nike Air Max or Manolo Blahnik. I think drawing pins have gone out of fashion these days, because when I was at school, people always had drawing pins stuck in their shoes — that'd make for interesting crime scene marks.

Some times, of course, on the basis of general pattern, a shoe can be
excluded
from having made a particular mark — a sole with a triangle block pattern isn't going to leave behind patterns of squares and circles. In general terms, the attributes normally compared in footwear mark comparisons usually include the following.

• The moulded sole pattern. This is classified on the basis of the elements that make up a sole pattern, such as bars, blocks, wavy ridges.
  
• The size of the shoe that made the crime mark. This only works where the entire sole can be seen. In cases where marks are not representative of the whole sole, for example, a bit's missing because the wearer trod partly on the nice piece of white paper but partly on the carpet, things get a bit trickier. This isn't helped by the fact that some manufacturers use the same mould for shoes of different (albeit similar) size.
  
• The degree of wear present. In some cases, a transient pattern results from frictional forces causing abrasion as the wearer scuffs or drags the sole as part of their day-to-day activity. Although the pattern changes rapidly,
  it can be used to conclusively link a footwear item with a crime scene mark. This usually only happens when the shoes are seized by the police really soon after the crime, or if the shoes haven't been worn or worn very little since the time of the crime. This some times happens in serious crimes such as assault or murder, where the perpetrator doesn't want to risk ditching the shoes so they hide them some where. There was a murder case in the USA once where a pair of shoes worn at the time of the murder was thrown over the side of a bridge in winter. Instead of landing safely in the water, they became stuck on a ledge where they were found weeks and weeks later, perfectly serviceable from a forensic science examination point of view.
  
• The presence or absence of the individualising characteristics I mentioned earlier, bearing in mind that if there's a time delay between a mark being made and recovery of footwear, the shoes may have acquired additional damage features and ones that were present at the time of the incident could have been obliterated.
  

Part of what I do as an independent expert in footwear cases is review the work completed by the prosecution expert. Although I made it sound nice and easy, an eye for detail, particularly at the magnified or microscopic level, is crucial. You have to ‘get your eye in', as my grandpa would say. It's like looking at one of those 3-D pictures that were popular in the 1990s, where you have to go cross-eyed to see the picture but when you do, it all becomes clear. Examining footwear marks can be like that; one minute it's all just a mass of smears and
bits of pattern, the next it's slipped quietly into place and you feel pretty pleased with yourself.

Having decent (as in cool) shoes among your peer group has been pretty important for a long time; think back to the days of teddy boys and brothel creepers, winkle-pickers, pixie boots, Doc Martens, Converse All Stars, the list goes on. One of the things that makes footwear mark examination successful is the enormous range of trainers that have flooded the market. In the 1990s manufacturers saw an opportunity and started making lots of variations on a theme, some of which cost a small fortune. It was pretty handy because it meant lots of different shoes were made with different designs and, most importantly, different sole patterns. It helped that they were comfy to wear and had good grip, which came in handy for shimmying up walls and hopping fences.

Having the latest pair of Nikes used to be crucial to street cred and burglars tend to be young men to whom having cool shoes is important — put the two together and you have a sub-population up to no good wearing reasonably distinctive footwear. Work has recently been completed at the University of Leicester, England, which indicates Reebok Classic trainers were the most popular style of training shoe worn by burglars in the county of Nottinghamshire, which ties in very nicely with my knowledge of English burglaries. The research also found that burglars from poorer areas tended to wear more expensive shoes; burglars with a job had less expensive trainers than those who were unemployed. This leads me to wonder whether employed burglars did it for fun or to supplement their incomes? Did the unemployed burglars have an average income greater than the employed burglars because they
received more government benefits? Under standably perhaps, the study had no knowledge of whether said trainers had been stolen or bought legitimately.

A recent paper in the international science publication,
Nature,
could put a spanner in the works if anyone decided mass marketing of training or running shoes was bad for the general population. The paper discussed the issue of human beings running barefoot for thousands of years compared with the relatively recent advent and widespread use of modern running shoes.

The paper described how long-distance runners who usually run barefoot most often land on the fore-feet/ball area before bringing down their heel. By way of contrast, those who wear running shoes mostly land heel first because the shoe provides cushioning and slight elevation. Study of running technique showed that barefoot runners who landed on their ball region generated smaller collision forces when they landed on the ground than those wearing running shoes. The net conclusion was that the foot-landing technique used by barefoot runners could protect feet and lower limbs from some of the impact-related injuries from which many runners now suffer.

It's an interesting paper and probably no surprise. However, in forensic science we have come to rely on the massive variation in, and constantly changing patterns on, the soles of trainers/running shoes. These patterns have been immensely useful for identifying particular pairs of shoes connected with crime. Even narrowing it down to a particular brand and model can help. If there were fewer patterns because there were fewer trainers (resulting in greater numbers of shoes with the same sole pattern), burglary cases would be much more difficult to
solve, particularly Johnny Recidivist, doing 10 burglaries over a weekend. There's a counter-side to every thing, isn't there?

One of the first crime scenes I ever attended was a fire in South Auckland. As is often the case, it didn't stay as just a fire-related case; for me the most interesting aspect was the footwear mark. By the time we reached the house, some of the windows had been boarded up but every thing was pretty much as it had been shortly after the fire. The owner said someone had broken into his house, set a fire in the sitting room and then left the same way they'd come in. The insurance company was having none of it and said the owner had set the fire himself.

One of the first things we did was check for signs of forced entry; if there were any then it would add credibility to the owner's account of events, if there weren't then it was inconclusive at best or, in the eyes of the insurance company, support for the contention that the fire had been facilitated by the owner. We could see nothing untoward around any of the windows or most of the doors of the house.

However, when we looked at the back door, it was a different story. The back door was a simple, two-layer, hollow board construction with two hinges at one side and a handle and opening/locking mechanism in the usual location about halfway up the door. To the side of the handle and lock was what would be expected — a thumping great footwear mark from the sole of a fire officer's standard-issue boot. This was where entry had been forced by the fire service and was in accordance with the fire investigation report.

Just to the side and slightly below that very dominant mark
were two or three faint sole marks from some other type of footwear. The shapes and movement in the marks (that is, they looked scuffed and out of focus) were consistent with them having been made when the door had been
in situ
and prior to the fire officer kicking in the door. Although we couldn't put an age on the marks, it was some thing of interest and this case was really the first that sparked my interest in forensic science. Unfortunately for the house owner, the insurance company didn't find in his favour and they didn't pay out.