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Impression EvidenceImpression Evidence Recognition and CollectionRecognition and Collection CJI6111/MHS5611: Week 1CJI6111/MHS5611: Week 1

Welcome to the impression evidence class. This first week we will be discussing the basics of impression evidence as well as the recognition and collection of this type of evidence.

Types of Impression EvidenceTypes of Impression Evidence

►►FirearmsFirearms ►►Tool marksTool marks ►►FootwearFootwear ►►Tire tracksTire tracks ►►Latent FingerprintsLatent Fingerprints ►►Fabric ImpressionsFabric Impressions ►►Bite MarksBite Marks

There are a lot of different types of impression evidence, the types are practically endless. This list represents the major types of impression evidence. The types we will be discussing this week include firearms, toolmarks, footwear, and tiretrack evidence. The latent print information will be discussed in weeks 8 & 9 and the other types of impression evidence are beyond the scope of this class, but being aware of these types of evidence is always important.

Types of Impression EvidenceTypes of Impression Evidence

►► Impressed (Static) MarksImpressed (Static) Marks These marks have one direction of force and look like a These marks have one direction of force and look like a negative of what made the impression. (examples: shoe negative of what made the impression. (examples: shoe and tire impressions, hammer hitting wood, and tire impressions, hammer hitting wood, breechfacebreechface marks on fired casing, etc.)marks on fired casing, etc.)

►► Striated (Dynamic) MarksStriated (Dynamic) Marks These marks have two directions of force, both a These marks have two directions of force, both a downward force and a parallel force so the marks downward force and a parallel force so the marks appear like scrapes. (examples: rifling on bullets, appear like scrapes. (examples: rifling on bullets, cutting tools such as bolt cutters, screwdriver scraped cutting tools such as bolt cutters, screwdriver scraped over surface, etc.)over surface, etc.)

Described above are the two types of impression evidence. Impressed or static marks are types of marks that only have a downward direction of force. An example of this would be hitting a hammer on a surface and the impression of the hammer head is left behind. Striated or dynamic marks have a downward force as well as directional force. Think of the way hard boiled eggs look when you cut them with a knife. You can see the striations left there by the knife cutting through the egg whites, that is an example of a striated toolmark. Marks can also be a combination of both impressed and striated.

Impression MarksImpression Marks

►►The material that retains the impression The material that retains the impression mark must be softer than the tool leaving mark must be softer than the tool leaving the impression.the impression.

►►The impression marks left by a tool are a The impression marks left by a tool are a result of the random imperfections found on result of the random imperfections found on the tools that are a result of their the tools that are a result of their manufacture and usage.manufacture and usage.

In order for a tool to leave a mark, the tool must be harder than the surface it is marking. Some examples of this are a steel screwdriver on a brass door plate, a set of teeth in skin, or a shoe in sand. The basis that impression evidence can be identified to a particular object is a result of the manufacturing process as well as the use, abuse, and age that a item goes through. Casting, grinding, and polishing metal instruments along with using them results in small random imperfections that are observable differences from one tool to another. This has also been found to be true among consecutively made tools.

ToolmarkToolmark EvidenceEvidence

►►Marks of tools or of objects that have been Marks of tools or of objects that have been used as tools can be found at the scene of a used as tools can be found at the scene of a crime, especially in burglaries.crime, especially in burglaries.

►►These marks can be left in wood, metal, These marks can be left in wood, metal, putty, or paint.putty, or paint.

Marks of tools or of objects that have been used as tools can be found at the scene of a crime, especially in burglaries. These marks can be left in wood, metal, putty, or paint. The types of tools that can be used are knifes, screwdrivers, drill bits, cutters, crowbars, and pliers.

Preservation of Tool marksPreservation of Tool marks

►►Whenever possible, keep the tool mark in Whenever possible, keep the tool mark in itit’’s original form.s original form.

►►If submission of the whole object is not If submission of the whole object is not possible, several casts should be made of possible, several casts should be made of the impression after photographs have been the impression after photographs have been taken.taken.

If you can submit the object that has the toolmark, this is the best option. For small items such as door knobs, brass door plates, locks, and other small objects, this isn’t too difficult. For larger items submission to the lab isn’t always the best option. The tool mark should be photographed with a scale and oblique lighting, and several casts should be taken.

Preservation of ToolsPreservation of Tools

►►When suspect tools are found, they should When suspect tools are found, they should be packaged in a separate container from be packaged in a separate container from the impression, the best way is strapped the impression, the best way is strapped inside a sealed box.inside a sealed box.

►►Examine the tool to see if trace evidence is Examine the tool to see if trace evidence is present.present.

►►Never use the tool or place it against the Never use the tool or place it against the tool mark impression.tool mark impression.

When a suspect tool is found, it should be packaged in the condition it was found. If there is trace evidence on the surface though, that evidence should be photographed, documented and collected and packaged in another container for trace analysis. You should never try to use the tool or place the tool against the tool mark impression to see if that tool could have made the impression. This could damage the tool mark, transfer trace evidence, or even damage the characteristics of the tool. The examination process will be discussed further in week 4.

Firearms Firearms EvidenceEvidence

Next we will talk about the collection of Firearms evidence.

Firearms SafetyFirearms Safety

►►Always keep the muzzle pointed in a safe Always keep the muzzle pointed in a safe direction.direction.

►►Always keep your finger off the trigger until Always keep your finger off the trigger until ready for use.ready for use.

►►Always assume the firearms is loaded.Always assume the firearms is loaded. ►►Always keep action of gun open until ready Always keep action of gun open until ready

to fire.to fire.

When dealing with firearms, safety should be everyone’s number one concern. There have been incidences of weapons going off at crime scenes by not properly handling firearms. For this reasons, everyone should be familiar with the basics of firearms safety.

1. Always keep the muzzle pointed in a safe direction. If the gun is pointed in a safe direction, then even if it goes off it shouldn’t hit anyone.

2. Always keep your finger off the trigger unless you are ready to fire the firearm. This is the number one rule that is disobeyed in firearms safety. Of all the weapons that come into the lab, probably less than 1% of accidental discharges are actually caused by a malfunctioning firearm. The majority was because the individual pulled the trigger either by accident or unknowingly.

3. Always assume the firearm is loaded. Even if you know that the weapon is unloaded, if you treat it as if it is loaded then no accidents should happen.

4. Always keep the action of the gun open when examining the firearm. This is another way to insure no accidents will happen.

5. If you are not familiar with the type of firearm at a scene, then either ask someone who does or call the crime lab firearms unit.

Firearms SafetyFirearms Safety

The first step to unload most auto-loading firearms is to remove the source of ammunition. For revolvers, remove the ammunition in the cylinder. For all auto-loading weapons (pistols, rifles, and shotguns) remove the magazine or the ammunition in the magazine, if the magazine is not removable.

Firearms SafetyFirearms Safety

Next the chamber should be checked to see if it is loaded. If there is a cartridge in the chamber, it must be removed. Make sure that the magazine has already been removed otherwise, when you remove the cartridge in the chamber the firearm will automatically load a new cartridge when the slide is released.

Firearms SafetyFirearms Safety

Visually and physically (if able) check the chamber to make sure there is no cartridge in the chamber.

Firearms SafetyFirearms Safety

The weapon should then be strapped through the action to impede the firing mechanism and insure that it stays unloaded. The weapon should then be strapped inside a sealed gun box and sent to the lab. Another reason to place a strap through the action of the weapon is because several people may examine the weapon before it gets to the firearms examiner. Most of these individuals don’t have any training in firearms or firearms safety. Many of these individuals may even be afraid of firearms. You may know that the weapon has been unloaded, but for everyone else involved placing the strap in the action insures that everyone easily and safely knows that the weapon is unloaded as well.

Firearms SafetyFirearms Safety

Examples of rifles properly strapped

Firearms SafetyFirearms Safety

Select fire rifles properly strapped.

Firearms SafetyFirearms Safety

Here are some examples of properly strapped shotguns.

Packaging Possibly Loaded FirearmsPackaging Possibly Loaded Firearms

Here is some examples of how possibly loaded firearms should be packaged and sent to the lab. Both containers are specially designed to carry loaded weapons safely. Note in the bottom picture, pegs should never be placed in the trigger guard of the weapon.

Water GunsWater Guns

►► If a firearm is found in water packaging is If a firearm is found in water packaging is different than normal.different than normal.

1.1. Try to unload the weapon.Try to unload the weapon. 2.2. Place weapon in a container with the water it was Place weapon in a container with the water it was

found in.found in. 3.3. The lab should be notified that a water gun is being The lab should be notified that a water gun is being

submitted, since special attention has to be given to submitted, since special attention has to be given to this type of evidence.this type of evidence.

4.4. If the weapon is found in salt water, the weapon If the weapon is found in salt water, the weapon should be taken out of the salt water and transported should be taken out of the salt water and transported to the lab in fresh (unsalted) water.to the lab in fresh (unsalted) water.

If the weapon found in water is so rusted that unloading it is not possible, the weapon can be transported in water to the laboratory but the lab must be informed that the firearm may be loaded. Salt water is very corrosive on metal. If the weapon is left if salt water, by the time it is cleaned and examined by the lab, some or most of the parts may have become inoperable. This is why the weapon should be removed from the salt water and placed in fresh water.

Packaging Firearms EvidencePackaging Firearms Evidence

Each casing and projectile should be documented as to location and item number and packaged in separate containers. The containers should be marked with the appropriate information. Remember to collect fired casings, spent projectiles and projectile fragments, shotgun cartridges, shotgun components and shot, as well as unfired cartridges that may be present at the scene. Never put marks on the bullets or casings. Important identifying marks could be obliterated and make an identification impossible. Also, never use a metal tool to dig out a projectile. The area around the projectile should be removed first. Then the projectile carefully removed by breaking apart the surrounding material.

Footwear EvidenceFootwear Evidence

Next we will discuss the collection of Footwear and Tire Evidence.

Footwear EvidenceFootwear Evidence

►► Information Provided by Footwear Impressions:

Type, make and description of shoe

Approximate or precise size of footwear

Possible number of suspects involved in the crime, and path through and away from crime scene

There is a lot of valuable information that footwear impressions can provide in an investigation. It can provide the type, make and description of the suspect shoe. It can give the approximate and sometimes the precise size of the shoe, and the possible number of suspects involved in the crime and the path that they took through the crime scene. It’s also possible to identify a specific shoe as having made an impression.

DefinitionsDefinitions

► Footwear impression evidence: Any surfaces that have retained certain characteristics from the adding or removal of material by impressing against a shoe’s outsole.

► Casting: Filling of a 3-dimensional footwear impression with materials that will take on and retain the characteristics left by the shoe which made it.

► Lift: To transfer an impression from its original surface for the purpose of recovering it from the crime scene, through the use of adhesive tape, gelatin or electrostatic lifter.

► Fixatives: A spray or powder applied cautiously to a footwear impression prior to casting, to prevent it from loss of detail when the casting materials is applied to it.

The next two slides list some important definitions associated with shoe and tire impression evidence.

DefinitionsDefinitions ► Two-dimensional Footwear Impression - An impression, which for all

practical purposes, has the dimensions of length and width but not a significant depth.

► Two-dimensional footwear impressions may result from either the addition or subtraction of material.

► Possible materials to find impressions in include: Dust, oils, dirt and various liquids, including blood.

► Three-dimensional Footwear Impression - An impression with the dimension of length, width, and depth.

Prior to Collecting the EvidencePrior to Collecting the Evidence

►Thoroughly document the footwear impression in notes, photographs, and in the crime scene sketch.

►Make a retaining wall to keep casting material inside the area of interest.

Before lifting or casting a footwear impression it needs to be documented and photographed. Sometimes when lifting an impression or casting an impression the results are not successful. This being said, if you have already documented and photographed the impression you will still have information to give to the examiner. When taking pictures of the footwear impression remember to place the camera vertically over the impression with a tripod and a scale placed next to the impression. The film plane should be parallel to the impression so as not to cause distortion. Footwear and tire impressions require film that can captures fine detail. For that reason, use a fine-grained 35mm film in color and black & white. If digital cameras are used they should be set on fine, large format, and raw or tiff type file. One thing to remember about a digital camera though, most mid-priced or lower cameras do not have the resolution or photographic quality for impression examination. Since technology changes constantly, if you have questions regarding the use of digital cameras and impression evidence, call your local laboratory to see what their requirements are. If the bottom of the impression is noticeably deeper than the rest of the impression the scale should be brought down to the same level as the bottom of the impression. To capture the fine detail in the impression, oblique lighting with a flash should be used.

TwoTwo--dimensionaldimensional Footwear ImpressionsFootwear Impressions

Materials that can be used to lift 2Materials that can be used to lift 2--D D impressionsimpressions

HighHighYesYesHighHighInexpensiveInexpensiveGelatin LifterGelatin Lifter

NoneNoneYesYesHighHighInexpensiveInexpensiveAdhesive Adhesive LifterLifter

NoneNoneNoNoHighHighExpensiveExpensiveElectrostatic Electrostatic Dust LifterDust Lifter

PorosityPorosityDurableDurableDetailDetailCostCost

*Porosity is a concern when attempting to chemically enhance a 2-D footwear impression. Gelatin lifters typically are too porous to be chemically enhanced.*

Listed above are three common ways to lift 2-D footwear impressions and the pros and cons associated with each. Each of the different ways will be discussed in further detail later.

Electrostatic Lifter

Pathfinder Electrostatic Lifter

An electrostatic lifter can lift dry dust prints off of floors or walls. It has excellent detail that can be seen in the impression. The drawbacks to using an electrostatic lifter is that the lifts are fragile and can be damaged.

Gelatin LiftersGelatin Lifters

Gelatin lifters are fairly inexpensive and provide great detail and are easy to use. They come in several different colors to provide optimal contrast. Sometimes with gelatin lifters you can lift the same impression several times. One down side to gelatin is that they are porous, so chemical processing after the impression has been lifted is difficult because the gelatin will soak up the dye along with the impression. Gelatin lifters are good to use when lifting wet impressions. Care should be taken to not stretch the lifter when placing it over the impression. This could distort the impression.

Adhesive LiftersAdhesive Lifters

Wide fingerprint tape can also be used to lift footwear impressions in dust or those latent lifts that have been made visible with fingerprint powder. Many companies sell fingerprint lifting tape in widths suitable for footwear impressions. The white and black cards the tape is placed on are also available in wide widths. Narrow tape should be avoided because several pieces will have to be used to lift the entire print and the seams created by multiple pieces of tape can obscure individual detail for the examiner.

Casting Three Dimensional Casting Three Dimensional Footwear ImpressionsFootwear Impressions

Benefits of a CastBenefits of a Cast

► A good quality cast provides more comparative information than a photograph of a 3-D impression.

► Casts can capture the fine detail not readily visible in photographs.

► They are actual size; no re-sizing is necessary.

► Sufficient fine detail recorded in the cast can be compared directly to the shoe, possibly resulting in an identification.

Casts have several benefits over photographs. A good quality cast provides more comparative information than a photograph because a photograph is a 2-D representation of a 3-D item, where as, a cast is the positive impression of the actual shoe. Casts can also capture fine detail that may not be captured in the photograph. This can include details on the walls of the impression that you can’t see in a photo. In photographs you have to have a scale so that the photos can be sized 1 to 1. In a cast there is no need because the cast is the actual size of the impression. You can also compare the cast directly to the shoe. Making standards is not always necessary.

Materials used for casting:Materials used for casting:

YesYesHighHighInexpensiveInexpensiveDental StoneDental Stone

NoNoHighHighInexpensiveInexpensivePlaster of ParisPlaster of Paris

DurableDurableDetail Detail PresentPresent

CostCost

It use to be very common to use plaster of paris when collecting 3-D footwear impressions. There are several problems when using it though. It does reproduce a high degree of detail, but the media is very fragile so cleaning the cast is harder than with dental stone. Also, plaster of paris is very brittle, so the cast had to be reinforced with sticks or other items. Sometimes the items used to reinforce the cast could hold moisture and cause the cast to break anyway. Dental stone is easy to purchase. You can buy it from all the major crime scene companies or you could order it from your local dentist or dental supply company. It is fairly inexpensive, produces a high degree of detail and is very durable.

Dental Stone Cast Vs. Plaster of Paris

Fine detail can be recovered in the cast of a footwear impression

Here you can see the difference in dental stone versus plaster of paris. Although the plaster does have a lot of detail you can see scratches where the cast was cleaned and some of the parallel lines have lost their detail. The Dental Stone cast has retained its detail and is much easier to work with.

Preparing a Footwear CastPreparing a Footwear Cast

►► Remember to always photograph the impression Remember to always photograph the impression before casting.before casting.

►► For best results itFor best results it’’s always better to have casting s always better to have casting materials prematerials pre--measured and stored in zipmeasured and stored in zip--lock lock bags.bags.

►► You want to have the casting material to be the You want to have the casting material to be the consistency of thin pancake batter with all lumps consistency of thin pancake batter with all lumps removed.removed.

►► For the average footwear impression, use about 2 For the average footwear impression, use about 2 pounds of casting material and approximately 10pounds of casting material and approximately 10-- 12 oz of water.12 oz of water.

The best way to prepare a cast at a crime scene is to have pre-measured amounts of casting material already in zip-lock bags. The water can then be added to the zip-lock bag, the bag is then closed, and the mixture can be mixed by hand until all lumps are removed. Remember that once the water is added to the dental stone, a finite amount of time is available until the material hardens.

Things to RememberThings to Remember

► Once casting material is combined with water, it must be mixed quickly and completely in the bag to prevent setting prior to pouring the cast.

► Pour the cast indirectly so as not to disturb any of the fine detail letting the dental stone flow into the impression and following the pour behind the folw.

► Material can be kept in pre-measured ziploc bags and mixed with water when needed.

► Due to the strength of modern casting material, less casting material is needed to achieve the same durability as with Plaster of Paris.

Also, for the average footwear impression a barrier is not needed when using Dental Stone. If the impression is on a hill, a retaining wall can be placed near the impression so that the casting material will stay where it is needed. Always remember to document an photograph the impression properly before casting it.

Here is an example of a footwear impression prior to casting. The impression was properly documented and photograph, then cast. You can see the results of the cast and the detail that is present. Both photographs and casts should be submitted for examination.

When your cast is hardening the following information can be written directly in the back of your cast. Your name, date, time, an arrow pointing in the direction of travel, an arrow pointing in the direction of North and the impression number. The cast should be left to dry for at least 30 minutes. When the cast is lifted, the dirt adhering to the cast should be left there until the cast has been allowed to dry for 24 hours. It can then be packaged in a breathable box and handled with care. Generally the examiner will clean the cast once it is submitted to the lab with water and a non-abrasive brush. Try to avoid the temptation of cleaning the cast off before it has been able to dry thoroughly. If the cast is washed off while it is still damp, some of the fine detail can be lost.

Footwear CastingFootwear Casting

►►Check out this website demonstration by Check out this website demonstration by Evident on Photographing and casting Evident on Photographing and casting footwear impression.footwear impression.

►►http://http://www.evidentcrimescene.com/cata/cawww.evidentcrimescene.com/cata/ca st/dscasting.htmlst/dscasting.html

Taking 2Taking 2--D Footwear D Footwear StandardsStandards

The Inkless MethodThe Inkless Method

When an examiner is comparing footwear lifts from the scene to the suspect shoes, standards of the shoe must be made. One easy way is to use the inkless method. It’s called inkless because the ink used does not stain the bottom of the shoes. It comes with a special paper that reacts to the ink and then turns black when the ink is applied.

Three Dimensional Three Dimensional Footwear StandardsFootwear Standards

BioBio--FoamFoam

Bio-foam is an excellent way to get 3-D standards. Bio-foam is expensive and is really only useful when it is not possible to get the suspect shoes. It does have a great amount of detail, but still is not as good as the real shoes.

Tire track EvidenceTire track Evidence

Finally we’ll talk about tire track evidence.

Why should you collect tire track Why should you collect tire track evidence?evidence?

► It is a representative of the tread pattern left in a soft medium that can be both photographed and cast.

► This evidence can eliminate other tires whose tread wear patterns display different characteristics from those at the crime scene.

► It provides good, incriminating forensic evidence once the correct vehicle is located.

Sometimes tire track evidence may not look like a lot of evidentiary value, but it may tell the examiner more than on first appearances. The direction the car was traveling in, the track width of the car, and the tread pattern are all good things that may be apparent.

Casts vs. PhotographsCasts vs. Photographs

► A good quality cast provides more comparative information than a photograph of a 3-D impression.

► Casts can capture the fine detail not readily visible in photographs.

► They are actual size; no re-sizing is necessary.

► Sufficient fine detail recorded in the cast can be compared directly to the tire, possibly resulting in an identification.

Photographs should always be taken and documentation of the tire track before casting is done, because casting the impression will destroy the evidence that was there and sometimes casting isn’t always successful. Casting does provide the best evidence for the examiner, because it is an exact representation of the tire track impression.

Casting ProceduresCasting Procedures

► Thoroughly document the tire impression in notes, photographs, and in the crime scene sketch.

► Make a retaining wall to keep casting material inside the area of interest.

► Casting material should be deflected off flat surface to reduce impact on impression when being poured.

► Having materials pre-measured and stored in the mixing bucket will help to save time and frustration.

When casting a tire impression, you should always start with documentation and photography. When taking pictures you should always remember to fill the frame with the impression, use a tripod, keep the camera parallel to the impression and have a ruler next to the impression.

How a tire impression is madeHow a tire impression is made

When a tire rolls over loose dirt the weight of the car compresses the dirt underneath and takes on the characteristics of the tire.

This shows a proper photograph of a tire impression. The impression fills the camera frame, the photo is in focus, a scale is in place, and lighting highlights the tread pattern.

When casting a tire impression, always try to cast 3 foot sections if it’s that long. After the photography and documentation is finished, use paint sticks to make two retaining walls. If there is any debris that has fallen into the impression remove it carefully.

Preparing the Dental StonePreparing the Dental Stone ►Measuring materials can be tricky and best

if you get a consistency of a thin pancake batter with all lumps removed.

► For a 6 X 36 inch cast, use about one box (25 pounds) of material with approximately half a gallon of water (8 cups) -- this is approximate and will depend on consistency of mixture.

Casting a tire impression requires a lot of dental stone. It also requires at least two people to pour the casting material. All these materials can be pre-measured and keep on hand to make the process easier.

Measuring water and mixing of casting material.

Measure out the water and pour it into the bucket. Make sure that all the lumps are removed and that it is the consistency of pancake batter. Always have extra water on hand in case it is needed. Depending on the weather outside more water may need to be added. Everything else should be set up prior to mixing, because once water and powder are mixed there is a finite amount of time to work with the dental stone before it starts to harden.

The piece of cardboard is held close to the impression and the casting material is pour onto the cardboard and allowed to flow into the impression. The cardboard lessens the force that the casting material flows into the impression. The casting material and cardboard are moved up and down the impression filling in all the impression detail.

After pouring the cast the following information should be written in the backside of the cast as it is starting to harden. The name, date, time, arrow pointing in the direction the vehicle was traveling in, an arrow pointing in the direction of North, and the impression number.

Let the cast dry for at least 30 minutes. Use your fingers to help loosen the edges of the cast by moving the dirt around the cast. When the cast has been lifted there will be a lot of dirt stuck to the cast. This dirt should not be removed until the cast has been able to dry for a full 24 hours. I should be packaged in a breathable container and handled with care.

Once the cast has been allowed to dry for at least 24 hours, it can be cleaned with water and a soft non-abrasive brush. When the cast is cleaned it can be directly compared to the suspect tire.