ABSTRACT

Background: Fingerprints are one of the individual characteristics that are very commonly found in crime scene. It’s of three types: patent, latent and plastic. The development of these latent prints using fuming methods have been discussed.

Main text: The fingerprints found at the scene of crime is not usually complete. They’re partial and are referred to as chance prints. These prints are usually latent i.e. hidden. Based on the type of surface they are present on, many physical methods like powder, chemical methods like ninhydrin & silver nitrate and fuming methods like iodine & cyanoacrylate can be used. This article mainly describes the fuming methods, iodine & cyanoacrylate.

Conclusion: Iodine fuming can be used on both porous and non-porous substrates whereas cyanoacrylate fuming is only used for non-porous substrates. Both fuming methods are widely used nowadays. It’s very effective. Iodine fuming is specially very inexpensive & non-destructive. But both methods need to be performed carefully, preferably under supervision.

INTRODUCTION

Fingerprints are a unique physical characteristic of a person. It’s one of the most reliable sources of identification of an individual. These are imprints formed due to the protruding ridges and valley grooves on our finger. They are also known as friction ridges since they help in providing friction on our palm and fingers to help us hold objects.

Friction ridges are formed between 6^th and 25^th week of foetal development. They remain persistent throughout an individual’s life unless it has been surgically altered or burned. Fingerprints are formed mainly due to the perspiration released by the sweat pores on the ridges. Such prints are usually not visible by the naked eye and are thus called as latent prints which means ‘hidden’. They can also consist of daily contaminants that are used like lotion, cosmetics, food, grease etc. There are also patent prints which are formed due to fingers covered in other substances like blood, paint etc. They are visible to the naked eye and hence are also known as visible prints. Our friction ridges can also form 3D impressions when pressed on soft, malleable solids like clay, molten wax, soap etc. These are known as plastic prints.

The latent prints need further processing to make it visible. These prints can be found on mainly two types of substrates, porous and non-porous. Porous surfaces like paper, cardboard or wood are absorbent in nature so the latent prints are absorbed by the substrate. Non-porous substrates include glass, metal, plastic on which the prints just remain, the substrates are impermeable hence they’re more vulnerable to environmental changes.

Fuming methods are used on both types of surfaces. It’s a type of method where the fumes of the reagent are made to come in contact with the surface where the latent prints are present.

Our sweat is made of 98% water. The rest consists of salt (NaCl), minerals like K, Ca, Mg, amino acids, metabolites like lactate, ammonia and urea. Due to a chemical reaction between the sweat and the fumes, the prints become visible. For both substrates, the chemical commonly used is Iodine whereas for non-porous substrates, Cyanoacrylate fuming is done.

PROCEDURE

Iodine fuming-

It’s one of the oldest and easiest methods. Iodine shows the property of sublimation i.e., when it directly converts from solid to gaseous state.

In lab, iodine fuming is done inside a chamber. The sample is suspended inside and we wait for the iodine fumes to fill the chamber. Some heating or hot water bath might be required for the process. After 5-10 minutes, we see development of yellowish-brown colour prints. Immediately the prints are photographed because the iodine fumes evaporate after sometime. It can be fixed using starch solution. Iodine reacts with starch to form a blue-black coloured complex, which can persist for weeks or months depending on the storage conditions. Recently, benzoflavone is being used. It fixes and darkens the print.

Print developed after Iodine fuming

Print fixed after treating with benzoflavone

Cyanoacrylate fuming-

Alkyl 2-cyanoacrylate is acrylate ester which has the triple-bonded carbon-nitrogen (cyano or nitrile) group bonded within an ester. Cyanoacrylate fuming is exclusive for non-porous surfaces. It is colloquially known as Super Glue fuming. This process is done in a chamber. The sample is placed in the chamber and liquid cyanoacrylate, which vaporises to turn to gas, adheres to the print. Here, cyanoacrylate reacts with the amino acid present in our sweat. The cyanoacrylate keeps building up on itself to form a 3D print. This process is called polymerisation. It gets accelerated due to the humidity in the chamber. The resulting print is transparent or white in colour.

This 3D print is viewed and photographed under oblique light. With this fuming process, we can often see minute details like pores.

Since the print is white in colour, it is usually enhanced using fluorescent dye stains like Ardrox, Rhodamine 6G, basic yellow 40.

Prints after cyanoacrylate fuming

CONCLUSION

For cyanoacrylate fuming, care should be taken to not overheat it as it produces toxic hydrogen cyanide. This method is very useful to develop prints on bullet casings, trigger on firearms. It can also be used on both fresh and old fingerprints on smooth or textured plastics.

We can conclude that these methods are hassle free and can be done in a non-professional setting, especially iodine crystal fuming. It’s inexpensive and non-destructive. Since the iodine fuming technique is non-destructive, other techniques like ninhydrin treatment can be used afterwards. But iodine fumes are toxic in nature so care needs to be taken while doing it in a non-professional environment.

REFERENCES

1.      Hillary Moses Daluz 2^nd edition. Fingerprint Analysis Laboratory Workbook. Chapter 12. Boba Raton, FL : CRC Press [2019] . ISBN: 978-1-138-48805-2

2.      Gurvinder Singh Bumbrah. Cyanoacrylate fuming method for detection of latent fingermarks: a review. Egyptian Journal Forensic Science. 2017; 7(1): 4.

3.      Deepak Pawar. Iodine Fuming for Latent Fingerprints. Forensic Fingerprint. 2020

4.      Dr. G. S. Sodhi, Mr. V. N. Sehgal, Dr. A. K. Gupta, Mrs. Vimal Rarh. Iodine Method for Detection of Latent Fingerprints. Fingerprints and Other Impressions. Pathshala. FSC_P3_M7.

5.      Ms Vinny Sharma , Prof. (Dr) Sally Lukose , Prof. (Dr.) G.S. Bajpai, Types of fingerprints, location, collection and preservation. Development: conventional and nonconventional methods. Forensic Science and Forensic Medicine. Pathshala. CRIMINOLOGY/FSFM/XX

6.      Niranjan H, Shweta R, Kapil R, Chanchal K, Rakesh M. Unconventional powder method is a useful technique to determine the latent fingerprint impressions. J Forensic Sci Res. 2022; 6: 045-048.

Author:

Ms Aishiki Sadhukhan

Intern ( Batch-2 2022)

Applied Forensic Research Sciences.