Serial Number Restoration Precision Forensic Testing Serial Number

Serial Number Restoration © Precision Forensic Testing

Serial Number – A unique number typically applied to an object by a manufacturer Serial Number Restoration – The practice of restoring an obliterated serial number by using scientific methods © Precision Forensic Testing

Commonly Marked Items n n Many items have serial numbers placed on them by the manufacturer. Stereos, computers, vehicles, televisions, and almost all electronic equipment have serial numbers. The discussion of this lecture will focus on firearms and serial numbers applied to them. Firearms are the most commonly encountered item in crime laboratories with obliterated serial numbers. The firearms are made from a variety of materials including aluminum alloy, stainless steel, and steel. © Precision Forensic Testing

Types of Serial Numbering Application Methods Serial numbers can be applied in a variety of methods. Each method has unique characteristics which enable them to be differentiated from each other. The method employed by a manufacturer is generally dictated by what is most economically efficient. If the manufacturer is already set up to do stampings, the serial number may be stamped. If the manufacturer uses laser etching to mark other parts of the firearm, they may use lasers to etch the serial number. © Precision Forensic Testing

Dot Matrix n Dot matrix engraved serial numbers are fairly shallow and are made by a succession of dots © Precision Forensic Testing

Dot Matrix - Examples © Precision Forensic Testing

Laser Engraving n Serial numbers engraved with a laser are shallow and have a “burned” appearance. © Precision Forensic Testing

Laser Engraving © Precision Forensic Testing

Stamped Serial Numbers n Stamped serial numbers are made by using a stamp with a positive impression of a number and applying sufficient pressure to impart a negative impression of the stamp on the object © Precision Forensic Testing

Stamped Serial Numbers - Theory n n When a serial number is stamped in metal, plastic deformation of that metal occurs After the force causing the deformation is removed, the impression remains © Precision Forensic Testing

Stamped Serial Numbers © Precision Forensic Testing

Stamped Serial Numbers - Theory n n n The compressed area at the base of the stamping is strained below the surface of the stamp mark The depth of the strained area is dependant on the type of metal. For example, the strained area of steel may be affected for approximately 6 times the depth of the stamp The purpose of stamping the metal is to impart a permanent number used for identifying that item © Precision Forensic Testing

Stamped Serial Numbers - Theory n n Stamping a serial number while the metal is below it’s recrystallization temperature is known as “Cold Working”. When metal is cold worked, the areas that are worked will change properties. These changes include: increased hardness and tensile strength. However, there are decreases in it’s malleability and ductility n n Additionally, the position of the metal in the electromotive series is raised which lowers it’s resistance to oxidation The lowered resistance to chemical oxidation allows for the use of acid to etch more efficiently in the area where the serial number was stamped. © Precision Forensic Testing

Obliteration n When serial numbers are obliterated, they are generally ground down beyond the lowest point of the original stamping. This results in the visible portion of the serial number being removed. By removing the serial number, criminals hope that the object can not be identified as having been stolen. © Precision Forensic Testing

Obliteration n n The serial number is no longer visible due to the removal of the top layer of the metal. The area below the obliterated layer is affected by the stamping process and is the reason serial number restoration is possible. © Precision Forensic Testing

Serial Number Restoration - Chemistry n n n Steel is comprised of iron and carbon. Additional elements such as nickel, manganese, chromium, cobalt, vanadium, and molybdenum are added to enhance it’s properties. Sulfur and phosphorus are typically present as impurities. The elements are bound at the atomic level Copper salts (Copper Chloride) are common in many metal etching reagents for the purpose of assisting in the oxidation of iron Anodic Reaction: Fe 0 Cathodic Reaction: Cu 2+ Fe 2+ + 2 e. Cu 0 + 2 e- © Precision Forensic Testing

Visualizing Restorations n n n The reason serial numbers appear when they are acid etched is due to specular reflection. Specular reflection – light reflecting off a smooth surface Diffuse reflection – light reflection off rough surfaces Specular Reflection Smooth Surface Diffuse reflection Rough Surface © Precision Forensic Testing

Serial Number Formula List n Acidic Ferric Chloride n n Turner’s Reagent 25 grams Ferric Chloride (Fe. Cl 3) 25 m. L Hydrochloric Acid (HCl) 100 m. L Water (H 2 O) n n Ferric Chloride n n 25 grams Ferric Chloride (Fe. Cl 3) 100 m. L Water (H 2 O) n Fry’s Reagent n n n 2. 5 grams Cupric Chloride (Cu. Cl 2) 40 m. L Hydrochloric Acid (HCl) 25 m. L Ethyl Alcohol (CH 3 CH 2 OH) 30 m. L Water (H 2 O) 25% Nitric Acid n n 75 m. L Water (H 2 O) 25 m. L conc. Nitric Acid (HNO 3) 90 grams Cupric Chloride (Cu. Cl 2) 120 ml Hydrochloric Acid (HCl) 100 m. L Water (H 2 O) © Precision Forensic Testing

Serial Number Restoration n An obliterated serial number typically has a surface that has been scratched so that the number is no longer recognizable © Precision Forensic Testing

Serial Number Restoration n n The first step in the process of restoring the serial number is to polish the surface by using sand paper in progressively finer grits. Polishing the surface will help in visualizing the serial number. © Precision Forensic Testing

Serial Number Restoration n Acid Etching – The acid reacts with the metal and produces hydrogen gas bubbles © Precision Forensic Testing

Serial Number Restoration n The result of the acid etching is a restored serial number. The dark appearance of the numbers is the result of diffuse reflection. © Precision Forensic Testing

Documentation n n The final step in performing a serial number restoration is documenting the recovered serial number. This can be done by writing down the numbers or photographing the results. Photographing serial number restoration may be difficult due to the lighting requirements. Additionally, the chemicals used to etch the metal should be documented in the notes. © Precision Forensic Testing

Case Studies n n n An ATV was suspected of having been stolen from a local dealership. When police attempted to read the VIN (Vehicle Identification Number) it was observed that it had been obliterated. The number in question was located on the engine © Precision Forensic Testing

Case Studies n The surface with the obliterated number was located on the top of the engine block © Precision Forensic Testing

Case Studies n n This is the area on top of the engine where the VIN number was stamped. The first step in the restoration process will be to sand it smooth. © Precision Forensic Testing

Case Studies n After the surface was sanded, Acidic Ferric Chloride was applied to the engine block. © Precision Forensic Testing

Case Studies n The Vehicle Identification Number was restored to H 310 E-06674. Using this information, police were able to verify the ATV was stolen and press charges against the suspect. H 31 0 E-06674 © Precision Forensic Testing

Case Studies n A shotgun was discovered under a couch during a drug raid. While attempting to locate a serial number, it was found to have been ground off. © Precision Forensic Testing

Case Studies n n The serial number on the shotgun has been totally ground off. Once again, the area is sanded smooth to give the best possible results © Precision Forensic Testing

Case Studies n 25% Nitric acid was applied to the area that had been

Case Studies n n A photograph of the serial number was enhanced to show the number. Documenting the restored serial number is important when the case goes to trial and it can be shown to a jury. H 9 2 4 8 50 © Precision Forensic Testing