Presentation developed by T. Trimpe

Impression evidence can be defined as objects or materials that have retained the characteristics of other objects through direct contact. Impressions are created when one object is pressed against another material with enough force to leave an impression of the object. Shoeprints, tool marks, tire tracks, bite marks, and marks on a fired bullet are several examples of impression evidence. Impressions may be found in or on many different types of materials. The quality of the impression depends on the object making the impression and the surface conditions, such as how hard or soft it is and what type of material it is (soil, mud, dust, concrete, grass, skin, etc.) Images: and CSI & Impressions What is impression evidence?

Collection Methods Investigators analyze the impression evidence to find unique characteristics to link shoes, tires, tools, and other objects found in a suspect’s possession to evidence at a crime scene. Collection of impression evidence can be accomplished using several methods: 2-D: This type of impression is documented using photography. Some impressions may be dusted with fingerprint powder to be photographed or lifted with tape. They may also be collected using an electrostatic dust lifting process. 3-D: This type of impression can be documented using photography as well as by casting, which involves using dental stone or a similar substance to preserve the dimensional characteristics of the print. Images: Example of Shoe Print in Bio-Foam Impression Foam

Tire tracks are important in forensic investigations and are usually found in road accident scenes or in the access and escape routes of other crime scenes. Tracks help investigators identify the type of vehicle that left them. Investigators may make ink prints of a tire or plaster casts of a track. They will also take photographs that can later be used to prove a match. Features to analyze: Tread pattern Width & depth of the tread pattern Unique characteristics due to the wear pattern or defects Images: Tire Track Evidence Tire databases are available help investigators determine the brand and model of the tire that left the impression, which can be used to determine the type of vehicle that made the tracks.

Certain defects or patterns may be left on a tool when it is made or used, which can be used to find matches between evidence at a crime scene and tools or objects found at a suspect’s home. Images: and Features to analyze: Dimensions of the impression Ridges or striation patterns Defects, such as nicks and chips Paint chips or metal shards left on a tool Tool marks can be classified two ways: (1)Impressions – As a tool hits a softer surface, the shape of the tool and imperfections in its surface may be left behind as an impression. (2)Scratches – As a tool moves across a surface, it may leave ridges or striations behind. NOTE: Some tool marks are a combination of both types. Tool Mark Evidence

Tool Marks A tool mark is considered to be any mark that is cut, gouge, or abrasion caused by a tool coming into contact with another object. A careful examination of the impression can reveal important class characteristics, such as the size and shape of the tool.

Tool Marks But it is the presence of any minute imperfections on a tool that imparts individuality to that tool. The shape and pattern of such imperfections are further modified by damage and wear during the life of the tool.

Tool Marks The comparison microscope is used to compare crime-scene toolmarks with test impressions made with the suspect tool. When practical, the entire object or the part of the object bearing the tool mark should be submitted to the crime laboratory for examination.

Tool Marks 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.

Tool marks on bones Tool marks on bones can identify the type of tool that was used in the crime and may isolate it down to individual evidence for a trial.

Other Impressions Impressions of other kinds, such as shoe, tire or fabric impressions, may be important evidence. Before any impression is moved or otherwise handled, it must be photographed (including a scale) to show all the observable details of the impression. If the impression is on a readily recoverable item, such as glass, paper, or floor tile, the evidence is transported intact to the laboratory.

Footprints and Tire Marks

Investigators can analyze a shoe print to determine its class, or the type and brand of shoe. They will also look for individual characteristics, such as wear patterns and specific damages or defects. Databases of shoe prints are available for investigators to help them determine the brand of shoe to provide leads for a case. Depending on the quality of the impression, investigators may be able to determine a person’s speed (walking vs. running) as well as estimate the size of a person based on the impression’s depth. Features to analyze: Tread patterns, size, and depth Wear patterns caused by the way a person walks Material defects or damage (nicks, cuts, etc.) Other trace materials, such as soil, tar, rocks, and paint that would indicate where a person has been Images: and Shoe Print Evidence Shoe Print in Bio-Foam Impression Foam STAMP Database

Other Impressions If the surface cannot be submitted to the laboratory, the investigator may be able to preserve the print in a manner similar to lifting a fingerprint.

Other Impressions When shoe and tire marks are impressed into soft earth at a crime scene, their preservation is best accomplished by photography and casting. In areas where a bloody footwear impression is very faint or where the subject has tracked through blood leaving a trail of bloody impressions, chemical enhancement can visualize latent or nearly invisible blood impressions.

Points of Comparison A sufficient number of points of comparison or the uniqueness of such points will support a finding that both the questioned and test impressions originated from one and only one source. New computer software and web sites may be able to assist in making shoe print and tire impression comparisons. Also, bite mark impressions on skin and foodstuffs have proven to be important evidence in a number of homicide and rape cases.

Toolmarks Tools often used in burglaries may leave a mark. Class characteristics: type, size, shape Individual characteristics: features from wear and damage

Matching Toolmarks ? ? Photography and casting are important to match tool with mark.

Ick.

Impressions Class characteristics— manufacturer, type, model, size Individual characteristics— wear patterns, nicks, marks, occlusions (like pebbles or sticks) Shoeprints

Impressions, continued Shoeprints Captured by oblique-angle photography or chemical enhancement; also by casting in soil, or lifting.

Footprint

Impressions, continued Treated much the same as shoeprints Class characteristics involve design, size, type, and model. Wear and damage cause defects that can lead to individualization. Tire Treads

Impressions, continued TreadMate is a database containing data on more than 5,000 vehicle tires and tread patterns. Tire Treads

Impressions, continued Result from assault or sexual attack, common in domestic violence Individual evidence, if enough impressions Bite marks were the prime evidence in the conviction of serial killer Ted Bundy. Bite Marks

Bite mark

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: Bite Mark Evidence Bite Mark Evidence Video

Bitemarks and Computer Analysis

Where is this bite mark located?

Most famous bite mark case of the 20 th century

Comparison of Bundy’s teeth Wax impression From victim

Impressions, continued Serial Numbers Restoration of serial numbers Items of value may have ID numbers stamped into them. Grinding is usually used to obliterate identification numbers. To restore ID numbers on metal, an acid etching solution is employed. HCl-CuCl 2

Image: It’s time to investigate some “impressive” evidence!