Tool Marks and ImpressionsTool Marks and Impressions

Tool MarkTool Mark

• Any impression, cut, gouge, or abrasion Any impression, cut, gouge, or abrasion caused by a tool coming into contact with caused by a tool coming into contact with another object.another object.

• Usually found at burglary scenes or Usually found at burglary scenes or scenes of forced entryscenes of forced entry

Comparing Tool MarksComparing Tool Marks

• Indented impression is left on the frame of Indented impression is left on the frame of a door or window as a result of prying with a door or window as a result of prying with a screwdriver or crowbara screwdriver or crowbar

• Close examination can reveal class Close examination can reveal class characteristics or the size and shape of characteristics or the size and shape of the toolthe tool

• Usually can’t connect the marks to one Usually can’t connect the marks to one tool unless there are random nicks or tool unless there are random nicks or breaks that the tool has acquiredbreaks that the tool has acquired

• The edges of a pry bar, chisel, screwdriver, The edges of a pry bar, chisel, screwdriver, knife or cutting tool display microscopic knife or cutting tool display microscopic irregularities that look like ridges and irregularities that look like ridges and valleysvalleys

• Left as a result of the machining process Left as a result of the machining process that is used to cut and finish toolsthat is used to cut and finish tools

• Damage and wear of the tool can also Damage and wear of the tool can also make imperfectionsmake imperfections

• The variety of patterns among these tools The variety of patterns among these tools makes it highly unlikely that any two will be makes it highly unlikely that any two will be identicalidentical

• We can use these imperfections to identify We can use these imperfections to identify individual toolsindividual tools

• When a tool is scraped against a softer When a tool is scraped against a softer surface it may cut a series of striated lines surface it may cut a series of striated lines that reflect the pattern of the tool’s edgethat reflect the pattern of the tool’s edge

• Compared using a comparison Compared using a comparison microscope with test tool marks made by microscope with test tool marks made by the suspected weaponthe suspected weapon

Problems with Tool Mark Problems with Tool Mark ComparisonsComparisons

• Difficult to duplicate the tool mark left at Difficult to duplicate the tool mark left at the crime scene in the laboratorythe crime scene in the laboratory

• Must make test tool marks at various Must make test tool marks at various angles and at different pressuresangles and at different pressures

Collecting Tool Mark EvidenceCollecting Tool Mark Evidence

• Then entire object or part of the object bearing Then entire object or part of the object bearing the tool mark should be submitted to the the tool mark should be submitted to the laboratory as evidencelaboratory as evidence

• When you can’t remove the tool mark from a When you can’t remove the tool mark from a crime scene you resort to taking a picture of it crime scene you resort to taking a picture of it and make a cast of the markand make a cast of the mark

• Liquid silicone is the best material to use for Liquid silicone is the best material to use for castingcasting

• A lot of detail can be lost when you are forced to A lot of detail can be lost when you are forced to use a photograph and a castuse a photograph and a cast

• Never attempt to fit the suspect tool into the Never attempt to fit the suspect tool into the tool mark this could alter the mark and tool mark this could alter the mark and question the integrity of the evidencequestion the integrity of the evidence

• Suspect tool and mark are packaged in Suspect tool and mark are packaged in separate containers to keep from separate containers to keep from destroying their individual characteristicsdestroying their individual characteristics

• Can be trace evidence like paint chips on Can be trace evidence like paint chips on the tool or impressionthe tool or impression

• Must be careful when handling and Must be careful when handling and packaging the evidence so you don’t lose packaging the evidence so you don’t lose any potential trace evidenceany potential trace evidence

ImpressionsImpressions• Can be a shoe, tire, or fabric impressionCan be a shoe, tire, or fabric impression

• Preserving impressionsPreserving impressions– Impression is photographed first from the top and at Impression is photographed first from the top and at

various angles and in relation to the crime scenevarious angles and in relation to the crime scene

• Lifting impressionsLifting impressions– When an impression is found on a surface that When an impression is found on a surface that

cannot be submitted to the laboratory we can lift the cannot be submitted to the laboratory we can lift the impressionimpression

Lifting ImpressionsLifting Impressions

• Place a lifting material over entire Place a lifting material over entire impression and use a fingerprint roller to impression and use a fingerprint roller to eliminate any air pockets before lifting the eliminate any air pockets before lifting the impressionsimpressions

• Can use a portable electrostatic lifting Can use a portable electrostatic lifting devicedevice

Portable Electrostatic Lifting Device Portable Electrostatic Lifting Device Continued . . .Continued . . .

• Place a sheet of mylar film on top of Place a sheet of mylar film on top of impression and film is pressed against it with impression and film is pressed against it with a rollera roller

• High voltage electrode of the electrostatic unit High voltage electrode of the electrostatic unit is placed in contact with the film and the unit’s is placed in contact with the film and the unit’s earth electrodes are placed against a metal earth electrodes are placed against a metal plateplate

• Charge difference develops between the Charge difference develops between the mylar film and the surface below the mylar film and the surface below the impression so the impression is attached to impression so the impression is attached to the lifting filmthe lifting film

Electrostatic Lifting FilmElectrostatic Lifting Film

Electrostatic Lifting DeviceElectrostatic Lifting Device

Casting ImpressionsCasting Impressions

• Shoe and tire marks impressed into the Shoe and tire marks impressed into the earth are best preserved by photographs earth are best preserved by photographs or castingor casting

• Class I dental stone is the best material to Class I dental stone is the best material to use for castinguse for casting

• Cast has to air dry for 24 to 48 hours Cast has to air dry for 24 to 48 hours before it is shipped to the forensics labbefore it is shipped to the forensics lab

Casting Footwear Impression Evidence

                                                                     

                                                                                                         

(Fig. 7)

                                                                     

                                                                                                         

(Fig. 8)

Pouring Procedure Place a form around the impression, if needed (Fig. 8) Pour the mixture onto the large spoon or stirring stick while holding the spoon or stick to the side of the impression. (Fig. 9,10) Allow the impression to dry a minimum of 30 minutes. Pertinent information, case number, date, time, location, etc. can be written on the cast after it is dry. (Fig. 16)

Carefully remove the form from the cast. (Fig. 11) The cast must be carefully lifted. (Fig. 12) Place a knife one inch from the form and stick it directly into the ground under the cast. Gently pry upwards. This should allow the cast to break free cleanly

from the surface.

                                                                                     

                                                                                         (Fig. 11)

                                                                                     

                                                                                         (Fig. 12)

Carefully remove the form from the cast. (Fig. 11) The cast must be carefully lifted. (Fig. 12) Place a knife one inch from the form and stick it directly into the ground under the cast. Gently pry upwards. This should allow the cast to break free cleanly from the surface.

Do not clean the cast until has been allowed to dry 24-48 hours. (Fig. 13) Package the cast in a box or other porous packaging material. Package it securely to ensure that it is not broken during transport. Do not package a cast in plastic.

Pertinent information, case number, date, time, location, etc. can be written on the cast after it is dry.

Comparing ImpressionsComparing Impressions

• Only possible when an item suspected of making Only possible when an item suspected of making that impression is recoveredthat impression is recovered

• Test impressions may be made for comparisonTest impressions may be made for comparison• Look for class characteristics: Size, shape and Look for class characteristics: Size, shape and

designdesign– Tell you if the impression was made by a particular Tell you if the impression was made by a particular

shoe, tire or garmentshoe, tire or garment

• Then look for individual characteristics: wears, Then look for individual characteristics: wears, cuts, gouges, or other damagecuts, gouges, or other damage– Can narrow down the impression to one sourceCan narrow down the impression to one source

SICARSICAR

• Shoeprint Image Capture and RetrievalShoeprint Image Capture and Retrieval• Shoeprint databaseShoeprint database• Searches known and unknown footwear Searches known and unknown footwear

files for comparison against footwear files for comparison against footwear specimensspecimens

• Can tell you the type of shoeCan tell you the type of shoe• Also compares shoe print to suspect shoe Also compares shoe print to suspect shoe

prints from other crimes to see if they are prints from other crimes to see if they are a matcha match

Bite marksBite marks

• Human bite mark impressions on foodstuff Human bite mark impressions on foodstuff and skin is another type of impression that and skin is another type of impression that can be used for comparisoncan be used for comparison