Tool Marks and Impressions

Tool Mark Any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object. Usually found at burglary scenes or scenes of forced entry

Comparing Tool Marks Indented impression is left on the frame of a door or window as a result of prying with a screwdriver or crowbar Close examination can reveal class characteristics or the size and shape of the tool Usually can’t connect the marks to one tool unless there are random nicks or breaks that the tool has acquired

The edges of a pry bar, chisel, screwdriver, knife or cutting tool display microscopic irregularities that look like ridges and valleys Left as a result of the machining process that is used to cut and finish tools Damage and wear of the tool can also make imperfections The variety of patterns among these tools makes it highly unlikely that any two will be identical We can use these imperfections to identify individual tools

When a tool is scraped against a softer surface it may cut a series of striated lines that reflect the pattern of the tool’s edge Compared using a comparison microscope with test tool marks made by the suspected weapon

Problems with Tool Mark Comparisons Difficult to duplicate the tool mark left at the crime scene in the laboratory Must make test tool marks at various angles and at different pressures

Collecting Tool Mark Evidence Then entire object or part of the object bearing the tool mark should be submitted to the laboratory as evidence When you can’t remove the tool mark from a crime scene you resort to taking a picture of it and make a cast of the mark Liquid silicone is the best material to use for casting A lot of detail can be lost when you are forced to use a photograph and a cast

Never attempt to fit the suspect tool into the tool mark this could alter the mark and question the integrity of the evidence Suspect tool and mark are packaged in separate containers to keep from destroying their individual characteristics Can be trace evidence like paint chips on the tool or impression Must be careful when handling and packaging the evidence so you don’t lose any potential trace evidence

Impressions Can be a shoe, tire, or fabric impression Preserving impressions Impression is photographed first from the top and at various angles and in relation to the crime scene Lifting impressions When an impression is found on a surface that cannot be submitted to the laboratory we can lift the impression

Lifting Impressions Place a lifting material over entire impression and use a fingerprint roller to eliminate any air pockets before lifting the impressions Can use a portable electrostatic lifting device

Portable Electrostatic Lifting Device Continued . . . Place a sheet of mylar film on top of impression and film is pressed against it with a roller High voltage electrode of the electrostatic unit is placed in contact with the film and the unit’s earth electrodes are placed against a metal plate Charge difference develops between the mylar film and the surface below the impression so the impression is attached to the lifting film

Electrostatic Lifting Film

Electrostatic Lifting Device

Casting Impressions Shoe and tire marks impressed into the earth are best preserved by photographs or casting Class I dental stone is the best material to use for casting Cast has to air dry for 24 to 48 hours before 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) Casting Footwear Impression Evidence

Carefully remove the form from the cast. (Fig 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 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 Pertinent information, case number, date, time, location, etc. can be written on the cast after it is dry.

Comparing Impressions Only possible when an item suspected of making that impression is recovered Test impressions may be made for comparison Look for class characteristics: Size, shape and design Tell you if the impression was made by a particular shoe, tire or garment Then look for individual characteristics: wears, cuts, gouges, or other damage Can narrow down the impression to one source

SICAR Shoeprint Image Capture and Retrieval Shoeprint database Searches known and unknown footwear files for comparison against footwear specimens Can tell you the type of shoe Also compares shoe print to suspect shoe prints from other crimes to see if they are a match

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