Impression Evidence Tools Tracks Tires and Lips Mrs

Impression Evidence: Tools, Tracks, Tires, and Lips Mrs. Schultz

What is Impression Evidence? • Impression evidence is when an object is pressed against a surface and a transfer of characteristics from one to the other occurs. • Fingerprints, footwear, tire tracks, and tool marks are common examples of impression evidence.

Impression Evidence: Tool Marks • A tool mark is made when some type of tool creates an impression, cut, scratch, or abrasion in another surface. • Even if you don’t have the tool, you might be able to match marks at other crime scenes. • Most often, tool marks are found in burglary cases. (Particularly screw drivers and crowbars).

Impression Evidence • Most tool marks are used to determine class characteristics. • Worn tools may have chips or uneven surfaces allowing for individual characteristics. • Markings from a crime scene can be compared to markings made in the lab with a suspected tool.

To make a marking… • An investigator will make several test marks at various angles with various levels of pressure. • They will also make test marks on a variety of surfaces.

Recovering Tool Marks • If possible, bring the mark in. • If it is not possible, photograph and then make a cast of the mark. • Casting material could be silicone rubber or other filled plastics. • Under no circumstances should the investigator try to fit a recovered tool into the mark. Why not? The impression may be altered. Trace evidence on the tool may be lost. The integrity of the evidence is compromised.

Follow this story taken from http: //www. firearmsid. com/Case%20 Profiles/Toolmark. ID/toolmark. htm • The steering column of a car was broken into using some kind of tool.

A suspect was found nearby with this screwdriver

Tool marks were found

A cast was made…you can’t fit a steering column under the microscope

A standard was made using the screwdriver To the left is the tool mark standard. To the right is the tool mark standard cast.

The standard cast and tool mark cast were compared. • The comparison under 40 X. The standard is on the left. Do you think it is a match?

Impression Evidence in Dust • The first step is to photograph it both alone and with a scale inserted. • There are two methods to lift impressions in dust: 1. Apply a lifting material, such as clear tape. Remove air bubbles with a roller and lift. 2. In electrostatic lifting, place a plastic coated metal sheet over the impression. Apply a negative charge to the sheet. Positively charged dust is attracted to the sheet.

Electrostatic Dust Lifting http: //www. crime-scene-investigator. net/Shoe. Impression. Skin. html http: //www. materials. qmw. ac. uk/events/tastercourses/images/2006/Materials%20 with%20 Forensic_electro. jpg

Impression Evidence in Soft Earth • The first step is to photograph it both alone and with a scale inserted. • The second step is to make a cast using silicone rubber or dental stone.

Retrieving a Tire Track Using Dental Stone http: //www. jeffreycreid. com/impressions/Impression_tire_snow_prints/impressions_tire_ and_snow_tracks. htm

Impression Evidence: Shoe Prints http: //www. uri. edu/pharmacy/crime_lab/dental%20 stone%20 lifting. jpg

To measure a tire track vs. a tire tread… To measure a tire track width To measure a tire tread width • Measure from the middle of the front two tires and/or from the middle of the back two tires. • Measure from the edge of the tire to the other edge of the tire of the front and/or rear tires. Track width Tread width

• By the way, on average, a person’s foot is 15% on his or her total height. If you have a print, you can estimate the height of the suspect.

Let’s Try…. . • Remove shoes and measure your height. • Measure the length of your left foot from the wall to the tip of the big toe. • Divide the length of your left foot by your height. Multiply the quotient by 100. What do you get?

A couple of other things… • Plaster of Paris is no longer used because it crumbles too easily. • Tracks in snow must be sprayed with wax before using a casting material as the material heats during curing and would destroy the impression.

And – did you know your lip print is unique as well? • You could have – – – Short vertical lines Long vertical lines Crisscross patterns Diamond patterns Branching lines http: //www. q 80 s. com/lip-prints-on-the-school-bathroom-mirror/