Serial Numbers and Fingerprints Quiz 3 Flashcards
Commonly Stamped Items
Firearms, electronics, farm equipment, machinery, and vehicles.
Serial Number Crimes
Federal and state law make it a violation to alter or remove identifying data.
Theft and illegal use of items cause offenders to remove this data so ownership cannot be traced.
Theory of Serial Number Restoration
Once metal has been stamped or impressed, the composition of it is changed forever due to the stress applied on the metal.
This allows for serial number restoration.
Serial Number Definition
A unique number applied to an object by a manufacturer.
Unique number vary based on manufacturers by numeric or alpha characters.
What can serial numbers tell us?
Date stamp of manufacturer.
Location of manufacturing.
Sequence of manufacturing.
Who the manufacturer is.
Most Commonly Marked Items in Crime Lab
Firearms with obliterated serial numbers.
Purpose of Serial Numbers
Quality Control: Identifies defective products.
Unique Identity: Item individuality.
Deterrent Against Theft: Assists in the possibility of recovering stolen items.
Serial Number Application Methods
Can be applied by a variety of methods.
Each method imparts unique characteristics that can be differentiated from one another.
Manufacturers general use most economically efficient method for them.
Types of Serial Number Application Methods
Dot Matrix Engraving.
Laser Engraving.
Stamped Engraving
Dot Matrix Engraving
Shallow and are made by a rapid progression of dots.
Laser Engraving
Shallow and often show a burned appearance on the metal.
Branding effect.
Stamped Engraving
Most common type of engraving encountered in a crime lab.
Made using a stamp that creates a positive impression on the object.
Plastic Deformation
Occurs when serial number is stamped in metal.
After force causing deformation is removed, the impression remains.
An engineering term meaning “permanent deformation” or irreversible changes due to force.
Metal Distortion
Occurs due to the force or pressure applied to a surface of metal.
Depth is dependent on the strain through the surface of the metal.
Purpose of stamping is to impart a permanent impression on the metal.
Obliteration
The process of making a surface or object undecipherable by wearing away.
Often occurs by grinding down most visible surface of serial number.
Common Types of Obliteration
Grinding. Pinging. Over-stamping. Drilling. Welding.
Serial Number Restoration Methods
Most common is chemical restoration.
Others include: Non-destructive, bar code decryption (manual), automatic decoding.
Chemical Restoration Method
Uses chemical etchants (acids) on the surface of smooth metal.
Acidic ferric chloride mixture.
Visualizing Restorations
Serial numbers are viewed when they are acid etched due to specular reflection and diffuse reflection.
Specular Reflection
The ability to view the light reflecting off a smooth surface.
Diffuse Reflection
The ability to view light reflecting off a rough surface.
This dark area that reveals number is result of diffuse reflection.
Steps in the Restoration Process
- Polish the surface (provides specular reflection and a consistent reflection of light.
- Apply acid which will react with metal and produce hydrogen gas bubbles.
- Documentation
Rinse and Repeat
Acid etching may restore serial number the first time, but if not the step can be repeated.
Serial Number Restoration Documentation
Accomplished by: Extensive note-taking. Chemicals used. Order of operations. Photographs.
Decryption of Barcode Identifiers
Step by step process for restoring obliterated serial barcode identifiers using conventional processing and automatic decryption methods.
What is a Barcode?
Series of patterned bars and spaces of at least 2 different widths.
Encryption into a computer text of a legible serial number.
Arrangement and Sequencing of Barcodes
Denote alpha/numeric/symbolic characters converted to a computer text.
History of the Barcode
Development begain in 1948.
First application by railroad industry.
1981 accepted Barcode 39 for by DOD for items sold to military.
Code 39 Specifications
Fixed pattern of elements that represent single character.
All codes include one start and stop character in addition to serial number characters.
Code 39 Characters
Each character has 9 elements, 3 of which are wider than the others.
9 bars = 1 character.
1 character = 5 dark bars and 4 light bars.
Code 39 Symbols
43 character choices:
0-9, A-B, *$/+%-
Start and stop characters always an asterisk.
Interpreting Barcode
9 elements = “W & N” pattern.
Bar pattern will correspond with a character denoted in the Code 39 Key.
Steps for Automatic Decoding
- use Code 39 barcode reader.
- Scan barcode.
- Must have complete barcode.
- If portions of bars are missing, take a picture and fill in bars, then scan again.
Chemical Restoration of Barcodes
Use chemical etch method with low corrosive rate.
If successful, manually decrypt for quality assurance.
If partially successful, attempt to scan with code 39 reader or manually decrypt.
Techniques for Restoring Barcodes
Automatic Decoding.
Chemical Processing.
Manual Decryption.
Steps for Manual Decryption: Step 1
- Inspect barcode and make sure you have portions of each bar.
Steps for Manual Decryption: Step 2
- Determine if all bars are present.
Know structure: 7 characters.
One character = 5 dark bars.
Have total of 45 dark bars.
Steps for Manual Decryption: Step 3
Separate Character Units.
Start at left and count 5 black bars.
Place line in space between black bars.
Steps for Manual Decryption: Step 4
Count wide and narrow patterns for each section.
Steps for Manual Decryption: Step 5
Use code 39 key.
Find corresponding W or N pattern on chart.
Determine each character.
