CRIMINAL JUSTICE FORENSICS

This assignment will give you the opportunity to create and evaluate your own impression evidence. As you have read in your textbook, pattern evidence is, for the most part, examined by the naked eye.

YOUR ASSIGNMENT IS TO:

REVIEW THE TWO PHOTOS ABOVE VERY CLOSELY

Discuss what type of individualized pattern you see and how you would collect and preserve this evidence.

What information can be gleaned from this type of evidence?

The paper must be two full pages in length. Must be formatted according to APA style and cite all your resources in the text as well as on the references page.

SECTION 7.1 of The TEXTBOOK ABOUT INDIVIDUALIZED PATTERNS

Patterns for Individualization

Patterns for individualization are characteristic of evidence that can be unique among the members of their class. This can be very important associative evidence in an investigation. We might be able to figure out that a particular tire made a tire mark, or a particular piece of footwear made an impression, or that broken pieces of a headlight lens came from a specific car in a hit and run, which may tie a suspect to the scene of a crime. There are two major types of individualization patterns: physical match patterns and impressions.

Physical Matches

Physical match patterns are formed from the pieces of randomly broken objects and are sometimes called jigsaw fit matches. The patterns are like a picture puzzle. For instance, if a glass was broken and there weren’t too many pieces, it wouldn’t take long to figure out how the pieces fit back together to form the original glass. Even if some pieces were missing, it would be likely that at least a few pieces would fit together. Note that this works for solid objects that fracture in a random fashion. In cases of solid objects, these physical matches are also known as fracture matches.

Suppose that several pieces of a broken glass were found at a crime scene. Later, a suspect was developed and police searched his apartment. In the cuff of a pair of pants, a piece of glass was found. The lab performed an analysis and physically matched the pants-cuff piece to the glass pieces from the scene. This evidence goes a long way toward putting the owner of these pants at the scene around the time the glass was broken.

When the object that fractures is solid and breaks in a random fashion, the physical matching of the pieces is called direct, or sometimes primary. If an object or item isn’t solid or fractures in a way that doesn’t result in clean, smooth fracture surfaces—such as pieces of cut or torn fabric or a snapped piece of wood with ragged irregular ends—the physical match is called indirect, or secondary. Experts can work to try to fit these pieces back together, but even if the match looks right, there is uncertainty. It is much easier to imagine a piece of similar cut or torn fabric "matching" an unknown by chance than it is in the broken glass case. Experts will not generally say that secondary physical matches are true individualizations. Instead, they might say the pieces fit, and are consistent with having been part of the same original, but they cannot confirm a common origin.

Impressions

Another major type of individualization pattern is impressions. Impressions occur when two objects come in contact with one another, and one object leaves behind distinguishing markings on or in the other. There are three types of impressions, which are distinguished based on depth and how the marks are made. Impressions that are essentially stamped by an object into or onto another are called imprints if they are more or less flat (two-dimensional). They are called indentations if they have depth (three-dimensional character). For example, many fingerprints and tire impressions are imprints because they are left on hard surfaces. However, they can be indentations if they are left in a soft receiving medium, such as a fingerprint in soft tar, or a tire impression in soft soil. If the receiving surface is marked by an object or surface moving across it—in effect, being scratched by it—the marks are called striations. The markings on bullets that firearms examiners use to identify the gun from which a bullet came are striations. Any sliding toolmark, like a mark made by a screwdriver scraping across a latch plate on a door, is also a striation.

Patterns for Reconstruction

Patterns for reconstruction help create theories of the events that occurred at a scene. Reconstruction patterns include glass fractures, furniture and objects at a scene, tracks, trails, trajectories of projectiles, skid marks in auto accidents, and more. Fracture patterns in glass can help determine what caused the breakage. The distribution and condition of clothing and objects at scenes can help to determine what happened, if there was a struggle, movements of persons involved, and so forth. Tracks and trails can help show the direction of movement of people. Projectile trajectories, such as the path followed by a bullet in a shooting case, can help reconstruct the position of the weapon with respect to the target. Skid marks help automobile accident reconstructionists determine the direction and speed of vehicles just prior to an accident. Depending on the speed and direction of a vehicle at the time its brakes are applied, a tire skid mark with a particular length and direction is created. Documentation and measurements of the marks can help reconstruct direction and speed. There are computer programs now that assist traffic accident reconstruction specialists in these tasks.

Collection and Preservation of Pattern Evidence

There are different ways of collecting pattern evidence, depending on the markings or impressions left behind. Two important terms to know are positive and negative impressions. A positive impression is identical to the object that made it, whereas a negative impression is its mirror image. The shoe prints left in the mud are negative impressions; they are negatives of the shoes’ soles. In this scenario, the positives would be the shoes’ soles. The same is true in the case of a tire indentation. This mark would be collected by casting. The resulting cast is a positive, like the tire that made the mark, so the cast can be compared to the tire.

In general, imprint markings are collected by first photographing the mark with and without a scale present, and then either collecting the whole object that has the mark, or if that is not possible, by tape lifting. If the imprint markings are made up of dirt or grease or other residues, they can be lifted from a surface with sticky tape (similar to Scotch® tape). The tape must be placed onto the surface with care, to avoid creating any bubbles. A rubber roller can help in this process. Then the tape is carefully lifted, so as to avoid any damage to or distortion of the mark, and placed onto a contrasting backing surface. A black mark, for example, would be placed onto a white backing surface. This item is then labeled with the usual required information and placed into a paper or plastic container and sealed. Lifting tapes of various sizes and appropriate backings are commercially available.

Indentation markings must also be photographed. As mentioned earlier, side lighting helps give the impression better contrast. After photography, the mark is cast. For this purpose, dental stone is used. This is a special finely ground plaster used by dentists to make molds for restorations. It is mixed with water to make a pancake-batter consistency mixture, then poured into the indentation so as not to disturb any of the detail present. Once it hardens, it can be removed. It captures fine detail quite well. In addition to labeling the packaging of a cast, the collector can scratch a case number or item number into the top side of the hardening dental stone. There are special types of casting materials for tool marks, for marks in snow, and other specific types of marks. Tool marks are discussed in a later chapter, but for now, dental stone is not capable of capturing the very fine detail in a tool mark (like a striation mark made by a screw driver on a lock plate). There are silicone-based materials commercially available that are better suited for this task. These silicone-based materials can also be used for indentation-type fingerprints, such as a fingerprint in wax. Indentation markings in snow pose a problem because dental stone gives off heat as it hardens, and the heat can melt the snow and destroy the impression detail. Products like Snow Print Wax can be sprayed onto the mark to protect it from this effect. An indentation impression is a negative, and so the cast of the impression is a positive. Accordingly, the cast can be compared directly with the tire or footwear or other item that is thought to have made the indentation.

Both in collecting evidence and in thinking about how pattern comparisons are done, it is important to remember that comparisons must be made between like impressions. Left with left, right with right, positive with positive, and negative with negative. The detailed individual characteristics that help in individualizing the mark must be in the same orientation as the original object that made the mark (or as its mirror image). Sometimes, this requires that the lab create a known from the suspected item in order to make the comparison. For example, a lifted footwear impression from a scene would be compared with an inked impression of the suspected footwear made in the laboratory.