Impressions

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Tool Marks

Tool marks are made when a harder object comes in contact with a softer object, leaving marks on it.

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What is a Tool Mark? A tool mark is

considered to be any impression, cut, scratch, gouge, or abrasion caused by a tool coming into contact with another object.

For example, if you attempted to pry open a locked window with a screwdriver, the screwdriver would leave a tool mark on the window and windowsill.

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Usually Involve Forcible Entry

Most often, tool marks are encountered at burglary scenes that involve forcible entry into a building or safe.

Typically, an indented impression is left on the frame of a door or window as a result of the prying action of a screwdriver or crowbar.

One of the first things an investigator looks for at a suspect’s home is the suspect’s toolbox.

Any tools in the commission o f a crime leave unique scratch marks behind.

These striation marks can be used to match a tool to an object it came into contact with at the crime scene.

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A careful examination of these impressions can reveal important class

characteristics. . . That is, the size and shape

of the tool. However, they rarely reveal

any significant individual characteristics that could permit the examiner to individualize the mark to a single tool.

Such characteristics, when they do exist, usually take the form of discernible random nicks and breaks that the tool has acquired through wear and use.

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Microscopic Irregularities Just as the machined

surfaces of a firearm are impressed with random striations during its manufacture, the edges of a pry bar, chisel, screwdriver, knife, and cutting tool will likewise display a series of microscopic irregularities having the appearance of ridges and valleys.

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The Machining Process

Such markings are left as a result of the machining processes used to cut and finish tools.

These markings are called striation marks.

The shape and pattern of such minute imperfections are further modified by damage and wear during the life of the tool.

When a screwdriver is first made, the microscopic imperfections in the blade make it unique.

As it is used, more imperfections are added and the blade becomes more unique.

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Imperfections Cause Individuality Considering the

unending variety of patterns that the hills and valleys can assume, it is highly unlikely that any two tools will be identical.

Hence, it is the presence of these minute imperfections that imparts individuality to each tool.

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One of the major problems associated with tool mark comparisons is the difficulty in duplicating in the lab the tool mark left at the crime scene.

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Striations If the edge of a tool is

scraped against a softer surface, it may cut a series of striated lines that reflect that pattern of the tool’s edge.

Markings left in this manner are compared in the lab through a comparison microscope with test tool marks made from the suspect tool.

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Positive Comparisons Once at the crime lab, a

cast is made of the scratch marks left on the window lock from the forced entry.

The result can be a positive comparison, and hence a definitive association of the tool with the evidence mark, when a sufficient quantity of striations match between the evidence and test markings.

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Test Marks A thorough comparison requires

the preparation of a series of test marks obtained by applying the suspect tool at various angles and pressures to a soft metal surface (lead is commonly used).

The cast and the lead brick with the scrapings are placed under a comparison microscope to see if the striation marks match.

This approach gives the examiner ample opportunity to duplicate many of the details of the original evidence markings.

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Bring the entire object to the crime lab.

Whenever practical, the entire object or part of the object bearing a tool mark should be submitted to the crime lab for examination.

When removal of the tool mark is impractical, the only recourse left, is to photograph the marked area to scale and make a cast of the mark.

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Photograph the mark. However, even under

the most optimum conditions, the clarity of many of the tool mark’s minute details will be lost or obscured in a photograph or cast.

Of course, this will reduce the possibility that the criminalist could individualize the mark to a single tool.

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Use liquid silicone or dental stone for casting.

Under these circumstances, liquid silicone casting material or dental plaster has been found to be the most satisfactory for reproducing most of the fine details of the mark.

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Under no circumstances . . .

Must the crime scene investigator attempt to fit the suspect tool into the tool mark.

Any contact between the tool and the marked surface may alter the mark and will, at the least, raise serious questions about the integrity of the evidence.

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The Lindbergh Baby Kidnapping

In 1932 the infant son of Charles and Ann Lindbergh was kidnapped from his nursery. A handmade wooden ladder used to gain entrance to a second-floor window, a ransom note, some muddy footprints, and a chisel were the only clues left at the crime scene.

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The ransom was paid, but the infant was never returned.

His body was eventually found in the woods near the Lindbergh home.

A suspect, Richard Hauptmann, was eventually arrested.

One of the first things forensic investigator, Arthur Koehler looked for was Richard Hauptmann’s toolbox. . .

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In it he found . . .

The hand plane used to construct the homemade ladder.

The imperfections in the plane’s blade caused unique striation marks on any wood it was used on.

Test pieces of wood planed with this tool displayed the same striation marks found on the wooden ladder left at the Lindbergh home.

This proved that Richard Hauptmann’s plane was used to make the ladder used in the kidnapping.

The wood used to make the ladder used in the infants kidnapping was also matched to Richard Hauptmann’s attic.

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Packaging The suspect tool and

mark must be packaged in separate containers, with every precaution taken to avoid contact between the tool or mark with another hard surface.

Failure to properly protect the tool or mark from damage could result in the destruction of its individual characteristics.

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Furthermore The investigator must

bear in mind that the tool or its impression may contain valuable trace evidence.

Chips of paint adhering to the mark or tool provide perhaps the best example of how the transfer of trace physical evidence can occur as a result of using a tool to gain forcible entry into a building.

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Obviously The presence of

trace evidence greatly enhances the evidential value of the tool or its mark and requires that special care be taken in the handling and packaging of the evidence to avoid the loss or destruction of these items.

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Impressions

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Impressions can sometimes be discovered in the most unusual places. A man was found dead in the early

morning hours on the side of a road in Binghamton, NY – the responding police officers could tell just from the condition of the body that he had been the victim of a hit and run accident.

There had been a rainstorm that night, so no tire tracks were visible. . .

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There was also an absence of any skid marks . . . Indicating that the driver had not

stopped for the pedestrian. In a search of the crime scene the

police noticed a van parked on the side of the road, and on closer inspection, saw that there was a man asleep behind the wheel. . .

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The police knocked on the car window and proceeded to question the driver . . . He explained that he was out driving in

the early hours of the morning and was too tired to make it home.

The rain was also a factor in his decision to pull over and rest.

He said that he had almost fallen asleep and lost control of the van.. . .

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It had fishtailed in the driving rain . . . And when he regained

control of the vehicle, he decided to pull over and get some sleep.

When the police looked at the other (passenger) side of the van, they were shocked to see the impression of the pedestrian in the side of the van.

The driver did not even know that he had struck someone.

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Another Story . . . Of toolmark blunders and the use of forensic impressions. . . .

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The steering column of a stolen vehicle had been broken open with some type of tool in order to reach the ignition and disable the steering wheel lock.

A suspect located near the vehicle was found to have a screwdriver in his backpack.

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The investigating officer submitted the steering column to the crime lab along with the screwdriver to see if it might have been used in the crime . . .

The steering column was examined, and an area of striated tool marks was found on a small internal part.

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A cast of the questioned tool mark was obtained using a dental rubber casting medium so that the tool mark could be examined microscopically – (its tough to put a steering column under a microscope!).

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Spacing between teeth in gripping or cutting instruments can play a major role in forensic tool mark

examinations. 

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A tool mark

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Evidence Collection of Impressions

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There are three materials commonly used in forensic science to make casts of tool marks and other impressions:

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1. Dental StoneA very fine grade of calcium sulfate (known as

alginate, gypsum, or Plaster of Paris) that was developed for dentists to take dental impressions.

Dental stone is normally the material of choice when making a cast of bite marks, shoeprints, and tire prints.

Dental stone is prepared by mixing about 2 parts alginate with 1 part water. The resulting paste is applied to the impression

and allowed to set for a few minutes to a few hours depending on size and temperature.

Chromatic dental stone changes color, letting you know when to apply the paste and when it has set.

In snow, a waxy substance called Snow Print Wax is first sprayed over the impression, and then the cast is made.

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2. Permlastic3. Polyvinylsiloxan Are both used to take the impressions of

smaller objects like bite marks or scratches left behind on a forced lock.

Both products consist of two tubes (base and a catalyst), which are connected so that equal amounts of each are dispensed.

The two components are mixed, and the paste is applied to the impression.

Both compounds polymerize in about ½ hour to form an elastomeric (rubbery) solid which can then be peeled off the object.

Both take extremely fine impressions.

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Footwear can also leave valuable impressions and prints behind at the crime scene. An electrostatic dust lifter can be used to

charge a plastic film that has been placed over a footwear impression.

The charged plastic lifts any dust particles from the impression, and they adhere to the film.

These devices work best in a dry environment.

Work well on paper, wood, carpet, linoleum, and concrete.

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If a footprint is in a mud puddle, you may use a turkey baster to drain excess water and use powder to dry the area before casting the print.

Casts must be carefully packaged in a soft resilient material that would prevent breakage, such as cotton or Styrofoam, etc. It is helpful to secure the cast so that it will not move during transport.

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There are many Internet sites that provide data for matching footwear prints and tire track impressions to the manufacturer.

http://members.aol.com/varfee/mastssite/index.html

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Footprint Cast Inked Footprint

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Once the print or impression has been taken, the forensic scientist can develop a great deal of class characteristic evidence. Measurements of the length and width of

footwear can be used to calculate the size of a shoe.

The pattern produced by the sole of the shoe can be used to determine the manufacturer.

A footwear print about 11.5 inches long and about 4.3 inches wide might indicate a size 8 ½ D shoe.

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The tread patterns are often specific to different manufacturers. Many popular sneaker manufacturers

actually put the name of the company (Addias, for example) in the tread design or the company symbol (Reebok often includes its two lines with a third intersecting logo).

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Once the suspect is apprehended, the forensic investigator is often asked if a positive match can be made between the suspect’s footwear and the print left behind at the crime scene.

All shoes of a certain type are the same when they come off the production line.

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However, once a person starts wearing a shoe, random and unique wear patterns begin to appear. Some people put more pressure on one

side of the foot than on the other, and the tread picks up cuts, scrapes, and foreign objects, which can make each footprint unique.

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The forensic scientist takes the suspects footwear, inks it on a pad, and presses it against a piece of white paper much as in taking a person’s fingerprint. The print is compared to any left at the

crime scene, and a point-by-point match can be presented to the court just as in the case of a fingerprint

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Tire Track Impressions

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Design Elements:

Grooves: around a tire

Sipe: small grooves

Slots: across a tire

Tread Wear Indicator: raised bar under design; shows after wear

Tire Impressions

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Noise Treatment:

If tire design was exactly repeated around the tire, noise would result.

Design repeated at different pitch lengths

Tire Impressions

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Tire Track Evidence:

Track width: measured from right center to left center

Track width of front tires and rear tires are not always the same.

Tire Impressions

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Tire Track Evidence:

Wheelbase: measured from front center to back center

Tire Impressions

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Tire Track Evidence:

Turning Diameter: Diameter of a circle made when the wheels are fully turned.

Tire Impressions

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Recovery of Tire Evidence:

Photos taken along with log of location.

Since tire tracks are variable along length (pitch), entire track should be photographed (examination quality) with overlapping photos.

Ruler included

Tire Impressions

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Recovery of Tire Evidence:

Cast can be made of 3-D impressions Long sections (3 feet) should be cast. Use dental stone

Tire Impressions

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Analysis of Tire Evidence:

Class Characteristics can be used to eliminate a suspected tire or suggest a tire could have made the track.

Size Tread design

Tire Impressions

Some wear marks

Class Characteristics:

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Analysis of Tire Evidence:

Class Characteristics can be used to eliminate a suspected tire or suggest a tire could have made the track.

Known tires collected. Inked or 3D impressions can be made for comparison.

Tire Impressions

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Analysis of Tire Evidence:

Similar to shoes, individual characteristics can be used to identify an exact tire.

Remember, individual characteristics change over time.

Tire Impressions

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C.A.S.T. Website address: http://members.aol.com/varfee/mastssite/index.html

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An identical process can also be used for a tire track print or impression. The width of the tread impression gives the

first number in the size of a tire. For example, the tire size 235/60R16 stands for a

tire that has a 235 mm wide tread with an aspect ratio (the ratio of the height of the sidewall of the tire to the width of the tread divided by 100) of 60.

It is also a radial and fits on a 16 inch diameter wheel.

Multiplying the decimal aspect ratio (the aspect ratio divided by 100) by the width of the tire gives the height of the sidewall of the tire.

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A tire impression left at a crime scene that was about 9.3 inches wide and showed a repeating imperfection mark every 84.7 inches of travel is

consistent with this size tire.

To figure the size of tire . . .

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To prove this, the width can be converted from inches to mm by multiplying by 25.4 mm/in.

Width (mm) = width (in) X 25.4 mm/in

= 9.3 inches x 25.4 mm/in = 236 mm This value is consistent with a size 235

tire.

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Tire sidewall height

The height of the sidewall = 9.3 (width in inches) x 60/100 (aspect ratio)

= 5.6 inches

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Tire Diameter

The diameter (height) of the tire is the diameter of the wheel plus twice the height of the sidewall.

Diameter = wheel diameter + 2 x sidewall height

= 16 inches + 2 x 5.6 = 27.2 inches

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Tire Circumference

The overall circumference of the tire is

Overall circumference = 3.14 x diameter

3.14 x 27.2 inches = 85.4 inches

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Any imperfections in the tire tread would be expected to repeat every 85.4 inches, which is consistent with what was found at the crime scene.

Exact widths and diameters of tires vary depending on the manufacturer and on inflation, so the numbers are always approximate.

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Tread patterns are often unique, and patented, for each manufacturer, so a brand of tire can often be determined from the tread pattern.

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As the vehicle is driven, the tires develop unique wear patterns. Some wear faster on the front tires, and some

on the back. Wear can take place more on the inside of the

tires, the middle, or the outside, and wear may show scalloping along the edges.

There may be random cuts, nicks, or stones in the tread.

These all leave unique impressions at the crime scene that can be used to positively associate the vehicle with the crime.

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Dental Forensics

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Did you know? The most famous incident where bite mark evidence led to a conviction, was in the case of the notorious serial killer, Ted Bundy. He was responsible for an undetermined number of murders between 1973 and 1978 and was finally tied to the murder of Lisa Levy through bites that he had inflicted on her body.

Investigators can analyze bite marks for characteristics to help them identify victims or suspects as well as to exclude others. Marks can be left on a victim’s skin or other objects, such as Styrofoam cups, gum, or foods. Saliva or blood may be left behind that can be tested for DNA. Dental records including x-rays can also provide useful information, especially when attempting to identify a victim.

Features to analyze:•Type of bite mark (human or animal)•Characteristics of the teeth (position, evidence of dental work, wear patterns, etc.)•Color of area to estimate how long ago the bite occurred (old or recent bite)• Swab for body fluids for DNA tests

Images: http://www.forensicdentistryonline.org/Forensic_pages_1/currentopic1.htm, http://www.trestonedental.co.uk/images/0303.jpg

Bite Mark Evidence

Bite Mark Evidence Video

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Dental forensics concerns the application of dentistry to law.

In criminal trials, dental forensics can be helpful in two ways: 1. to establish the identity of a homicide victim 2. to associate a suspect with a crime using bite

mark analysis.

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People can be identified by their teeth because everyone’s teeth are different. Since almost everyone has been to a dentist,

most people have a dental record. This makes teeth a better identifier than

fingerprints, since many people have never been fingerprinted.

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Teeth are unique to the individual. Items to look for: Restorations – amalgam, gold, resin,

porcelain Fillings – location, size, and shape

Gums Root canals Missing teeth Unerupted teeth Patterns of arrangement Appliances, dentures

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Teeth are extremely resistant to decomposition and damage.

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Impressions made of teeth, look different from one another, particularly if a person has missing teeth or fillings.

Criminalists can use tooth impressions to identify the perpetrator of a crime by matching an impression of his teeth with the marks he leaves (i.e. in a piece of gum, cheese, an apple, or on a victim, or even old bite marks can be used because they show up under ultraviolet light).

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Why identify?

Brings closure to family and friends. Body can be laid to rest according to

religious beliefs. Legal settlements of estate and

insurance Legal action if negligence or other

crime were involved.

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Fun Fact!

The first recorded American use of forensic dentistry to make a positive ID was in the case of Dr. Joseph Warren.

He was thought to have died in the Battle of Bunker Hill.

Skeletal remains were found with a dental implant.

The implant was made of silver and was taken to the silversmith who was thought to have made it.

This mad admitted to having personally crafted it for Dr. Warren.

The silversmith’s name was Paul Revere.

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The most famous bite mark case . . .

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Naming Victims

Forensic dentists play an important role in identifying the remains of victims from mass disasters, such as those in the 1995 bombing of the Oklahoma City federal building.

Dentists from across the country helped identify 25% of the human remains from the 1994 disaster.

In a similar case, dentists helped identify many of the victims from the 1994 crash of American Eagle ATR 72 in Indiana.

Even though only 9% of the victims’ teeth were recovered from the crash, those teeth were used to identify half of the victims.

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Bones and Teeth

In another case, a forensic dentist examined eleven of the seventeen victims of Jeffrey Dahmer, a serial killer.

This was a particularly gruesome task because Dahmer had disposed of the bodies by placing them in a 50 gallon drum of muriatic acid.

The acid dissolved all of the tissues from the bones as well as the roots of single rooted teeth.

What investigators found in and around Dahmer’s home were stacks of bones, skulls, and loose teeth.

Dentists were able to place the loose teeth back into the skulls from which they came, then match dental records to the teeth.

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Don’t Bite

Bite mark analysis is a new, exciting method of establishing a connection between a bite marks and a suspect.

Bite marks occur primarily in sex related crimes, child abuse, and assaults.

Even though bite marks often include only a limited number of teeth, those teeth that can be identified from the mark often yield significant information.

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Children

Children have 20 teeth, but they start to lose these when their adult teeth begin to grow.

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Adults

An adult should have 32 teeth (including the four wisdom teeth, which grow in the late teens/early 20’s.

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Adults Children

8 incisors 4 canines 8 premolars

(sometimes called bicuspids)

12 molars

8 incisors 4 canines 8 deciduous molars No premolars

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Please note: When you look at the tooth chart, you are looking into a person's mouth with the jaws open. You're facing the person, so their upper right jaw will be on the left of this image.

Teeth are numbered from 1 – 32.Start at upper right (1) and count across to upper left (16).Then move down to lower left (17) and across to lower right (32)

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Age

Forensic scientists can use teeth to estimate the age of a body.

A child has 20 teeth, which are gradually replaced between the ages of about 6 and 18, by which time he should have a full set of 32 adult teeth.

After this age, the teeth gradually wear down.

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Diet

The way in which teeth show signs of wear can suggest a person’s diet.

In some cases, teeth can indicate a person’s occupation (i.e. tailors, who hold pins between their teeth).

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Different teeth have different purposes: Incisors – next to the front teeth and look

like chisels – used to bite food. Canines – the sharp, pointed teeth next to

the incisors – used to tear food. Premolars – uneven flat surfaces for

grinding and chewing food. Molars – uneven flat surfaces for grinding

and chewing food.

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Dental X-rays

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Radiograph

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Diagram that shows primary (blue) and secondary (yellow) teeth erupting

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2 years old

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5 years old

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8 years old

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Ancestry

Generally, from skull appearance, forensic dentists can determine race within the three major groups:

Caucasoid, Mongoloid Negroid.

Additional characteristics such as shovel-shaped incisors and multi-cusped premolars, can also assist in determination of ancestry.

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Multi-cusped premolars can also assist in determination of ancestry

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Sex

Sex determination is usually based on cranial appearance, as no sex differences are apparent in the morphology of teeth.

Microscopic examination of teeth can confirm sex by the presence or absence of Y-chromatin and DNA analysis can also reveal sex.

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