Identification of Impressions of Metal Marking Punches

Arun G. Bhoi

Arun’s Institute of  Forensic Sciences, Research and Education, Kale Padal, Pune – 411 028 (India).

Email : arun.bhoi@gmail.com

(e-J. Foren. Crime Inv. 2011, 1, 1. Art. 1, 1^st Jan. 2011)

ABSTRACT

In this work physical characteristics studied to know whether engine and chassis numbers present on respective sites of  M/Cars are produced by the use of questioned punching nails or not ? The numbers present on the voucher plates (Questioned) comparatively studied with the test impressions produced by the questioned metal marking punches using microscopy. Imperfections, striations present thereon and its positioning at the ‘Clock-type Grid’ helped to correlate these.

KEY WORDS : punches, impression, digits, engine, chassis, number, clock-type grid, forensic.

INTRODUCTION

The M/Cars and the sets of metal marking punches used for punching digits were examined to know falsification in engine and chassis numbers, if any. The stamped impressions found on the various organs of vehicles such as engine, chassis and voucher plate were comparatively studied stamped impressions produced using questioned punches for their identity, individuality and similarity or dissimilarity. Microscopic examination was preferentially carried for doing this work.

EXPERIMENTAL

Physical Examination

The punched numbers – impressions (Questioned) were observed on the engine number site, chassis number site and voucher plate of the M/car vehicle. Being engine as a heavy – voluminous machinery and the chassis panel a long – one piece part of the vehicle, the punched numbers present on these were examined, in situ. Further, tracings of these numbers were taken on butter paper using soft graphite pencil. Supportingly, the numbers present at engine and chassis site were dusted with fine graphite powder and its images were lifted on the one inch broad transparent cellophane tape. Then, simulated (Test ) engine and chassis numbers were produced on 1mm thick  aluminum sheet using questioned metal marking punches. The tracings were taken, as also, the numbers were lifted on the cellophane tape.

Afterwards, the design and the shape of the “Questioned” and “Test” impressions were comparatively studied in situ and making use of tracings and lifted numbers present on cellophane tape. The dimensional parameters such as heights, widths, thicknesses, high-low joints of letters/digits, its spacing, length of script were minutely examined and the identity of the impressions of letters/digits was established. Overlaying of the tracings / lifted numbers of “Questioned” and “Test” letters/digits also helped to correlate these.

Microscopic Examination

Voucher plates were examined by this technique using “Metzer Comparison Microscope”. For this, voucher plates bearing punched Model No., Engine No., Chassis No. and Serial No. were removed from the cars. Further, the simulation impressions of the corresponding letters / digits were produced on 1mm aluminum sheet using the respective metal marking punches. Then, the impressions present on the impressions present on the voucher plate (Questioned) and the simulation impressions (Test) from the aluminum sheet were comparatively studied by keeping these on the moveable mounting stage of the microscope and using the illuminating light assembly. Because of the advantages of the good heights, widths and other characteristics the impressions of the higher case letters viz. “O”, “B” and “H” were selectively chosen for this examination.

Below discussed are some of the features used for correlating stamped impressions present on voucher plate and the test impressions of the higher case letters viz. “O”, “B” and “H”.

1. Individual Characteristics : The higher case letter “O” (Questioned) shows the characteristic curve at position –I.           (Fig. 1 (a)). Similar curve has also been seen on the test impression (Fig. 1 (b)).

Figure 1 : Microscopic View of  :  (a)    Impression of higher case letter “O” from Voucher plate  (b)   Test Impression

2. Imperfections : The imperfection seen as on the impression of higher case letter “O” (Questioned) at position –II, has good identity with that of “Test” impression (Fig. 1 (a) and (b)). This imperfection has resulted by the crack/defect present in the punching nail itself.

3. Irregularities in the Plateau: The higher case letter “B” is chosen for studying the irregularities in the plateau. The misalignment of plateau of terminus and that of upper helices is observed in “Questioned” impression of letter “B” at position “I” (Fig. 2 (a)). Also, at the site “II” (Fig. 2 (a)) the major irregularity (discontinuity) in the vertical leg is prominently noticed. These irregularities are also reproduced in “Test” impressions (Fig. 2 (b)).

Figure 2 : Microscopic View of  :  (a)Impression of higher case letter “B” from voucher plate  (b)Test Impression

4. Identical Striations : On the middle arm of letter “B” the striations are seen sequentially produced (Fig. 3). “Questioned” and “Test” impressions show the linear consistency.  The unevenness in the thickness (shown by the dashed line “——-”) at some of the places of the running boundaries, arms and legs of the letters studied is because of the lack of the application of the uniform forces at the time of producing the respective impressions using punches.

Figure 3 : Microscopic View of leg and arm portion of higher case letter “B” showing striations

(a)Questioned Impression   (b)Test Impression

5. Clock-type Grid : Study of higher case letter “H” based on clock-type grid examination helps to correlate the “Questioned” and “Test” (Simulation) impressions and identifies the instrument / marking punch applied there so.

Figure  4 : Microscopic View of higher case letter “H” with marked ‘Clock – type Grid’ pattern.

(a) Questioned Impression from Voucher plate   (b) Test Impression

In Fig. 4, the ridges at the joint of the horizontal arm with the left leg at “9” – O’ clock position and the line running parallel to to this leg crossing the line of “7” – O’ clock position confirms the identity and the individuality of the stamping device. Furthermore, the plateau defects positioning in between “11” – O’ clock and “12”  – O’  clock, as also, the presence of plateau defect in “6” and “7” – O’ clock position supplements it. The deformities in the plateau or at terminals are usually the after effects of the continual/repeated use of the punches for stamping.

RESULTS AND DISCUSSION

By physical, dimensional and superimposition studies the impressions in  “Questioned” and “Test” (simulation) impressions of the punching nails under examination can be correlated. The parameters explained makes one enable to find the match between the corresponding impressions. These may, also, help to judge dissimilarities, if any, in the impressions to be compared. But these examinations are not full proof to decide the origin of the stamped impressions. However, the proper and careful evaluation of the comparative data and the critical features studied microscopically and use of ‘Type-clock Grid’ made it very much certain to say that the “Questioned” and the corresponding “Test” are derived by application of the same punches from the set. The individual characteristics, defects, irregularities observed in the respective ‘PUNCH’, differentiates / correlates it and its impression/s with the others. Thus by avoiding the possibility of the stamped impression  matching with the impression coming from such other punching nail manufactured from the same ‘HOB’.

ACKNOWLEDGEMENT

Author’s thanks are due to Director, Directorate of Forensic Science Laboratories, Mumbai, State of Maharashtra, India.