Skip to 0 minutes and 10 secondsOther evidence types that are linked to impression evidence include footwear marks and tyre marks. These can potentially provide evidence linking a pair of shoes or a vehicle to a scene, as well as linking crime scenes to each other. This can provide intelligence information for law enforcement agencies when investigating, for example, serial offences if these types of evidence are present. Footwear marks, which are sometimes called shoe prints, are the marks left behind on the ground or another surface like a window sill or a chair because someone has run, walked, stood, or jumped onto that surface. You will sometimes hear people referring to footwear marks as footprints, but this is not the correct term. Footprints are marks left by your bare feet.
Skip to 1 minute and 1 secondTyre marks are impressions that are left on the ground from the tyres of a vehicle, which can also include motorbikes and bicycles. The different parts of the shoe are shown in the image, and you can get more information about different types of shoes when you follow the link on the website listed.
Skip to 1 minute and 20 secondsIn terms of impression evidence, the most important part of the shoe is the sole pattern. This is the pattern on the sole of your shoe that is transferred onto receiving surfaces, such as floors, carpets, and so on. Sole patterns can distinguish shoe types from each other and can be linked with brands of shoes. In a similar way to sole patterns, tyre tread patterns are the aspect of the tyre that are examined by forensic scientists in an attempt to provide information such as the make of the tyre that may be responsible for the recovered mark. Here, the scientists are recording details about the thread pattern left behind by the tyres.
Skip to 2 minutes and 7 secondsScene examiners can also, in some circumstances, use tyre tracks at a scene to provide information about the vehicle, such as the axle track and the wheel base. Recovering footwear marks and tyre tracks involves photography of the mark in situ, sometimes enhancement of the mark if they are difficult to see, and then subsequent recovery of the mark by lifting using specialist equipment or by making a cast of the mark. What technique is used depends on whether the mark is two dimensional-- for example, a mark left in blood or in dust-- or three dimensional-- a mark left in soil or snow. Sometimes marks can't easily be recovered-- for example, if they are on a door.
Skip to 2 minutes and 53 secondsAnd the door in its entirety may be taken to the forensic science laboratory. The video shows how three-dimensional marks-- in this case, tyre marks-- can be cast and recovered. On some occasions, it is very difficult to visualise marks prior to photography and recovery, and specialist chemicals are used to enhance the mark so that they can be seen. The images show enhancement of marks on fabrics made in blood, using chemicals called luminol and acid yellow seven. Once marks are recovered from a scene, they can be compared to sole patterns or tyre patterns held in a database or, if a shoe or a vehicle has been recovered, with marks prepared in the laboratory from those recovered items.
Skip to 3 minutes and 42 secondsSeized footwear is used to make comparison marks using straightforward laboratory techniques. This is done to produce marks of the same type as the recovered footwear marks, whether that is two-dimensional or three-dimensional. This way the marks are compared like for like. For tyre marks, a tracing of the mark is made from the tyres in the forensic garage as part of the examination of the vehicle, and this is then compared with marks recovered from a scene. In the same way that we talked about the two-mark comparison process, the comparison of footwear marks or tyre marks makes use of both class characteristics and individual characteristics.
Skip to 4 minutes and 23 secondsAs you will know from your own experiences, and if you look at your own shoes or the tyres of your car, footwear and tires have many different patterns, and these are used to characterise the shoe or tyre. These patterns can be used to classify a shoe or a tyre by type or, in some cases, by brand. Forensic science laboratories have databases of sole patterns and of tyre patterns that can be used to narrow down a recovered mark to a possible brand. These databases are updated as new bands come onto the marketplace. This is very useful for excluding potential footwear or tyres from an inquiry as possible sources of the recovered marks.
Skip to 5 minutes and 7 secondsThe footwear or tyre track comparison is made on the basis of similarities between the tread pattern or sole patterns of the marks recovered from the scene, and the marks made in the laboratory or on the database. The comparison may include observing common features within the patterns, making measurements of these features, and comparing regions of the marks which may contain damage or wear. Manufacturing flaws can be present in the sole of the shoe or in the tyre. These can appear in the recovered marks from scenes and the marks prepared for comparison purposes by the forensic scientists.
Skip to 5 minutes and 47 secondsWhile these may be used to narrow the field of possible shoes or tyres within a particular class, they are marks that can appear in a range of items all manufactured by the same tools. Individual characteristics, on the other hand, are specific to a particular shoe or tyre. These are produced both by everyday wear and by damage occurring in the course of normal use of the shoe or the tyre. In the image, you can see some of these wear and damage marks as they have occurred over time for this particular shoe. It is these marks, if present on a mark at a crime scene, that may be diagnostic for a specific tyre or item of footwear.
Skip to 6 minutes and 30 secondsIn footwear and tyre mark comparisons, just like toolmarks, it is important to know that the examination is subjective, and it is dependent on the opinion of the examiner. This means that it is quite possible that two examiners could come to different conclusions about the same footwear marks they are examining. Forensic scientists will often be quite cautious in their evaluation of this type of evidence as a result. This is a summary of the topics covered in this part of the course. It might also be worth visiting the website of the US Scientific Working Group for footwear and tyre marks.
Skip to 7 minutes and 8 secondsThey have some videos worth watching which will provide more information about the manufacture of shoes and other aspects of recovery and comparison of marks.
Now we look at footwear marks and tyre marks.
We have provided two links in the ‘see also’ resources at the bottom of this page. Both of these are relating to the materials in the video. The first is the link to the page describing the parts of the shoe and the second is a link to the US Scientific working group for shoeprint and tire tread evidence (SWGTREAD), where there are some videos (in the resource section) and other useful information to have a look at.
Footwear marks and tyre marks are important types of impression evidence as they have the potential of associating a vehicle or a shoe to a particular place from which the impression was recovered. The recovery of these impressions is not always straightforward and often will involve taking a plaster cast of the impression if it is three dimensional, or trying to lift and recover the mark if it is two dimensional.
In some circumstances the mark may have to be chemically enhanced - for example if it is made in blood or soil - and techniques similar to those involved with fingerprints can be used.
The interpretation of tyremarks and footwear marks follows a similar methodology to that of other impression evidence where class characteristics and individual characteristics are examined, compared and evaluated in light of the case circumstances. In these cases databases can also be used.
After you’ve watched the video the next activity provides you with a means to make your own footwear marks.
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