Analysis of Obliterated Vehicle Identification Numbers: Five Case Studies
Written by Dr. Mukesh Sharma & Dr. Shailendra Jha   

The investigation of vehicle theft often requires the restoration of erased or altered vehicle identification numbers. When vehicles are stolen, it is commonplace for engine numbers and chassis numbers to be erased, and new numbers may be created in order to escape detection. Generally the new numbers are punched into the metal in the same location as the original number. When the original engine number or chassis number of a vehicle is erased and a new number is punched on top, it is possible to find the original number using a technique to restore the erased number.

When a metal surface is punched, the metal becomes compressed and deformed; this resulting disturbance of the metal is called “cold working”. This increases hardness and decreases malleability and ductility of the metal. The resistance to oxidation and acid is very low. The affected part reacts more with acids than the surrounding, unaffected area of the metal.

The choice of chemicals used for the restoration of erased numbers depends on the nature of the metal. Mostly we come across stainless steel, mild steel, iron, cast iron, copper, brass, and German silver. The restoration of the number is quite time-consuming and as soon as the erased numbers are visualized, immediate photography is required. Otherwise, the numbers may not be seen again due to the action of chemicals on metal (Nickols, Heard).

This article provides some examples of chassis-number and engine-number restorations that utilized chemical processes. In these cases, the owners of the stolen vehicles (a car, three trucks, and one motorcycle) were identified on the basis of a forensic report. We have also provided a simplified flow chart to help determine the best chemical for the restoration of numbers on different metallic surfaces.


First of all, the forensic scientist must search out the exact locations of the engine number and chassis number, and then verify these locations from the makers or vendors of these vehicles. There are three types of markings commonly found: a) cast marks, b) engraved marks, and c) stamped or punched marks. These marks can be restored by applying the appropriate procedures and chemical reagents (Srinivasan).

There are a number of techniques used to obliterate identification marks that are typically encountered in India:

  • Filing or grinding—The original number is filed away or ground down with a power grinder, followed by polishing, and then over-stamping with a new number.
  • Peening—This involves hammering the surface with a round punch to hide the number.
  • Over-stamping—Here, a new number is simply stamped over the old.
  • Center-punching—The surface bearing the number is obliterated with a pointed punch.
  • Substitution—An iron plate bearing a new number is pasted or welded over the original surface.
  • Drilling—This removes the number and the surrounding metal with a drill. The cavity is usually filled up with either lead solder or welding material.
  • Welding—The surface is heated with either an oxy-acetylene welder or an arc-welder until the metal flows.
  • Occasionally an original finish will be given to a previously obliterated number surface.

Chemical Etching Method

The chemical etching method is the simplest and most effective method for restoring obliterated numbers. It is simple to apply and it requires no expensive equipment. It works well on any size or type of object. The techniques involved require considerable skill and great patience. The materials are potentially dangerous and should be used with full awareness of health and safety requirements.

In the case of motor vehicles, remove the engine from the vehicle if necessary for ease of access to the engine-number surface, and for better-quality photographs of the restoration process. Examine the metal surface after using acetone to clean away oil and dirt (FBI). The full process of restoration is explained with the help of the flow chart (Fig. 1).

Figure 1—This simple flow chart shows the authors' recommended method for restoration of numbers in metal.

Look for any disturbance in the background pattern. This pattern will be present either in the form of milled marks caused by grinding the surface before stamping the serial numbers, or cast marks produced during the manufacturing process. Even if no erasure is noticed, remove the paint over a wide area around the surface and check to see whether the portion carrying the chassis number was removed by cutting and then substituted with a metal plate bearing a new number (Katterwe).

Case I: Tata Xenon pickup truck

In this case, the driver of a Tata Xenon pickup truck was stopped by the police and subsequently found to be transporting 500 kg of Doda Chura (poppy straw—the dried, upper portion of the opium poppy, minus the seeds). Our team traveled to the district police station and examined the chassis and engine of the truck. It was evident that grinding and rubbing had been performed in the area of the chassis number. The number plate was missing from the engine. We were able to successfully restore the original numbers of the pickup truck.

The following process is utilized when peening is observed (Images 1.1-1.5): First, prepare the surface using a file to polish and clear the damage caused by the pointed punch. Next, treat the surface with the solution shown in the flow chart for the iron-based chassis. The solution can be applied continuously for about 9 to 12 hours, or over the course of 2 to 3 days for 5 hours per day. Photographs should be taken before and after each step to document the process.


The restored number of the chassis of the Tata Xenon pickup truck (Images 1.4-1.5):

* M A T 4 6 4 2 0 3 C S K 0 2 4 1 0 *

Case II: Trailer truck

In this case, an individual claimed that his trailer truck was stolen, and that the thief had tampered with the chassis and engine numbers and re-painted the vehicle. Our team treated the original position of the chassis number and the newly stamped chassis number. The original chassis number was revealed beneath the newly stamped numbers (Images 2.1-2.5)


The apparent chassis number prior to treatment (Image 2.3):

4 4 7 2 0 7 A S Z 3 0 0 5 3 6

The restored chassis number (Images 2.4-2.5):

4 4 7 2 0 7 M T Z 3 0 1 7 2 5

Our team was also able to trace the registration number under the re-painted trailer body (Image 2.2).

Case III: Truck

In this case, one truck was found in a jungle by a night surveillance team of the highway police. The number could not be traced by the police at that time, so the police called our team to examine the chassis number. Our team treated the newly stamped chassis number that was placed over the position of the original chassis number. Our experts recovered the original chassis number under the stamped numbers (Images 3.1-3.4).


The apparent chassis number prior to treatment (Image 3.2):

M A T 4 5 7 4 0 3 D 7 H 4 8 9 8 8

The restored chassis number (Images 3.3):

* M A T 4 1 6 4 7 1 A 7 E 2 1 9 9 4 *

The original location of the engine number was found at the rear-accessible location under the engine (Image 3.4).

Case IV: Truck

In this case, one truck was detained by the Road Transport Office during an inspection that found the registration certificate and other papers related to the truck did not match. Our spot-examination team treated the original position of the chassis number and the newly stamped chassis number. Our experts recovered the original chassis number under the stamped numbers (Images 4.1-4.4).


The apparent chassis number prior to treatment (Image 4.2):

4 2 6 0 3 1 D R Z 0 0 9 7 4 2

The restored chassis number (Image 4.3-4.4):

4 2 6 0 3 1 G S Z 7 2 9 7 7 0

Case V: Motorcycle

In this case, a motorcycle was stopped at a checkpoint when officials noticed the motorcycle did not display the same number on its chassis as it did on its engine. Our team treated the original positions of the chassis and engine numbers. In this case, the location of chassis number had been ground down, had a coating applied, and then a new number was stamped over the location of the original number. The original engine number was completely erased then a new number was stamped in the same spot. Our team restored both the chassis and engine numbers.


The apparent chassis number (see Image 5.2):

9 4 M 1 7 F 0 0 6 5 8

The restored chassis number (see Image 5.3):

0 2 M 2 0 F 3 7 6 4 *
* May be “4” or “9”

The apparent engine number (see Image 5.4 on Page 10):

9 4 M 1 7 E
0 0 7 1 7

The restored engine number (see Images 5.5-5.6 on Page 10):
0 2 M * 8 E
3 6 6 0 4
* cannot be deciphered

Through these examples, one can easily understand the process of restoration and role of this technique that is widely applicable in vehicle theft, smuggling, and violation of transportation laws in India.


As shown in the photographs for all five cases, the erased identification numbers on each vehicles’ chassis and engine were restored.

When serial numbers are stamped using metal letter or number punches or dies, the depth of distorted or altered material is necessarily very shallow. It will not exceed approximately 1 mm in metals. The impression is punched into the surface by hand and the depth of the impression varies, not only from letter to letter but also in different parts of a single letter. In addition, the erasure is made quickly and unevenly (Maxwell, Springer). Inevitably, some portions of the lettering will be erased below the depth of alteration to the point that no detail can be restored. Depth of restoration does not increase concurrently with the depth of the stamp mark.

The expert must learn by experience to identify numerals from the appearance of ghost fragments, provided the fragment contains a key portion of the numeral. These ghost fragments usually appear quickly during development and then disappear. It is necessary to watch the development closely and record all appearances as they are recognized. Once the etchant eats below the point where the crystalline structure of the metal has been altered by the stamping process, the number is lost forever.

About the Authors

This e-mail address is being protected from spam bots, you need JavaScript enabled to view it is Senior Scientific Officer and Assistant Director at the Regional Forensic Science Laboratory in Bharatpur, Rajasthan, India. He has published more than 110 research articles in international and national journals and at conferences. His areas of specialization are tool mark analysis, trace evidence analysis, forensic physics, and cyber forensics.

Dr. Shailendra Jha has worked in the field of forensic science for the last 32 years and has worked more than 4,000 cases, covering vehicle accidents, arson, vehicle identification numbers, cyber crime, video authentication, voice examination, and crime scene examination.


Cunliffe, F. and P. B. Piazza. Criminalistics and scientific investigations. New Jersey: Prentice-Hall pp. 209-214. (1980)

FBI Laboratory, Restoration of erased marks and alterations. Handbook of Forensic Science pp. 1-4. (1979)

Heard, B. J. Handbook of firearms and ballistics: Examining and interpreting forensic evidence. Chichester, England: J. Wiley pp. 213-221. (1997)

Katterwe H. The recovery of erased numbers in polymers. Journal of the Forensic Science Society 34, pp. 11-16. (1994)

Maxwell S. L. The application of heat treatment for the restoration of vehicle identification numbers. Prepared for the 10th Australian Int. Forensic Science Symposium and amended for the National Institute of Forensic Science Workshop. Canberra, May 18-20, 1993.

Nickols L. C. The scientific investigation of crime. London: Butterworth & Co. pp. 150-164. (1956)

Springer E. and P. Bergman. Applications of non-destructive testing (NDT) in vehicle forgery examinations. Journal of Forensic Sciences 39(3), pp. 751-757. (1994)

Srinivasan, G.J. and G. Thirunavukkarasu. Decipherment of an obliterated vehicle identification number. Journal of Forensic Sciences 41(1), pp. 163-165. (1996)

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