Journal of International - JIARMsimilarities or differences of patterns of the energy, frequency and amplitude distribution of the voice sample. For performing the spectrographic analysis

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JIARM VOLUME 1 ISSUE 3 (APRIL 2013) ISSN : 2320 – 5083

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VOICEPRINT EVIDENCE IN FORENSIC INVESTIGATION: A CASE STUDY

SURBHI MATHUR* NIRAJ A PANCHOLI**

JAYANTKUMAR M VYAS***

*Assistant Professor Jr., Gujarat Forensic Sciences University, Gandhinagar Gujarat, India **Scientific Assistant, Directorate of Forensic Science, Gandhinagar, Gujarat, India

***Director General, Gujarat Forensic Sciences University, Gandhinagar, Gujarat, India

ABSTRACT

Voiceprint evidence has always been a matter of controversy in our judicial system

because of the limitations imposed by various factors like background noise, channel

variations, distortions etc, in the process of identification. The proponents of the technique

constantly support the voiceprint identification while the other scientists believe that the

technique has not been sufficiently subjected to well-designed scientific experimentation to

access reliability. The basic principle behind voice identification resides on the premise that a

person’s voice is his or her individual characteristic which can uniquely identify them among a

group of similar sounding people either of same or different age groups. The voice

examination technique relies on several vocal parameters. The combined assessment of all

these factors will facilitate an expert with more accurate and precise results for framing

definite opinion. In this paper we will be discussing about an important case of Gujarat state,

where voice of the suspect recorded from a telephonic conversation, played a significant role

in identification of the criminal. The manuscript clearly outlines what it requires to

successfully examine voice evidences and how such conscientious efforts smoothens the

process of administration of justice.

KEYWORDS: Forensic Science, Voice, Voiceprint, Identification, Examination, Recognition

INTRODUCTION

Our Judicial system usually rely on the scientific clues and evidences for apprehending

criminals. The type of physical evidences which have gained popularity within the court of law

includes: DNA, fingerprint, ballistics, footprint, explosives, narcotics, questioned documents

etc. Some of these evidences has passed their test for degree of reliability and are now widely

accepted as evidence in judicial proceedings. Others however are still a subject of debate

regarding their scientific importance and reliability for evidentiary use. One of such

controversial evidence is voiceprint evidence1, 2. Due to the challenges faced by experts while


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analyzing the voice evidence, the court most of the time feels reluctant to admit such evidence

in legal proceedings. Poorly recorded/noisy samples, physical and emotional variability of

speaker, voice disguise, channel mismatch or mismatch in recording conditions are certain

factors which impose great limitation in the process of identification3, 4.

Despite of many drawbacks the need to identify a criminal on the basis of voice arises

from time to time in legal proceedings5, 6. In the present era, widely available facilities of

telephones, mobiles and tape recorders results in the misuse of the device and thus, making

them an efficient tool in commission of criminal offences such as kidnapping, extortion,

blackmail threats, obscene calls, anonymous calls, harassment calls, ransom calls, terrorist

calls, match fixing etc7. The criminals nowadays are more frequently misusing these modes of

communication, believing that they will remain incognito, and nobody would recognize them8.

In such cases, it is believed that the voice evidence plays a vital role in identification of the

perpetrator. Although DNA is considered as the most important evidence for criminal

investigation, but the truth is that DNA can’t talk.

The voice evidence is usually accepted as the secondary evidence supporting other scientific

facts in the court of law, but in offenses where the criminal catch aid of telephone or mobile

phone for accomplishing their illicit tasks, voice automatically becomes the primary and most

valuable evidence for linking the suspect and the crime. The aim of this paper is to reflect the

importance of voice evidence in criminal investigation, the steps taken by the expert to

overcome all the limitations and achieve precise and accurate results.

CASE

In January, 2007, 9 years old, Nayan Kachrola, son of a diamond polishing unit employee

from Navsari, Gujarat was abducted outside his school by his neighbour Parvez Rana. The

abductor demanded ransom of 50 Lac from the victim’s father. Nayan had died due to

breathlessness as his mouth was sealed with a surgical tape and his body was thrown along a

railway track.

The father of the victim recorded all the telephonic conversations made by him with the

kidnapper on his mobile phone. The recordings were then transferred to the CD, which were

finally submitted to the police for further investigation. The control voice of the suspect was

recorded at All India Radio (AIR), Surat in presence of the investigating officer and two

independent witnesses. All the recordings were then sent to the Directorate of Forensic

Science, Gandhinagar for examination.


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MATERIALS AND METHODS

Voice examination is a multifaceted process requiring the use of both aural and visual senses.

For lending on accurate and reliable conclusion, the voice expert should not only rely upon the

visual comparison of few words but also on every aspect of the words spoken, the way the

words flow together, how the words are being delivered, pronunciation, accent, dynamic

loudness and the pauses between them.

The details of the exhibits received in the above mentioned case are given in table 1. The

examination required was to perform the acoustic and phonetic analysis of unknown voice in

the questioned conversation and specimen given by the suspect and to determine whether the

two voice samples were originated from the same source or not.

Before the performing the analysis, the exemplars submitted for examination should

be properly evaluated for establishing their validity and reliability. In order to get

accurate results from speaker recognition, one must give more emphasis on following

factors:

The minimum duration of the collected samples should be of 60 seconds

The signal to noise ratio of the samples should be as greater as possible

The characteristics of the available instruments for identification

Properties of the voice involved

Delay in examination of samples


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The questioned and control recordings were then analyzed and compared, both audibly

and spectrographically, to find out the similarities and dissimilarities in their phonetic,

acoustic and linguistic features.

In auditory analysis the questioned as well as specimen voice of the suspect were

repeatedly heard by the experts, in order to measure the likeness or variations between

them, in terms of their linguistic and phonetic features like articulation rate, flow and

delivery of speech, degree of vowels and consonant formation, rhythm, striking time,

pauses etc. From repeated listening some clue words which were then subjected for

spectrographic analysis.

The spectrographic analysis enables the examiners to visually inspect and compare

similarities or differences of patterns of the energy, frequency and amplitude distribution

of the voice sample. For performing the spectrographic analysis the instrument called

CSL-4500 (Computerized speech lab model) was used. As the questioned and control

recordings were done in different recording conditions and different recording device,

variations in their spectrographic pattern and frequency formation were observed. In order

to avoid complications in analysis, sampling size and quantization rate of both the

questioned and control recordings was set at 11 KHz, 16 bit, mono. Also, the

transformation and storage of recorded data from one medium to other i.e. from mobile

phone to computer and finally to CD, resulted in the loss of some important data from the

samples. The problem of signal cutting at the positive phase of the waveform was

observed in case of control recording. The use of LPC Frequency Response Filters was

made to eliminate unwanted frequency and bandwidth informations. While comparing the

samples more emphasis was led on the vowel patterns and their frequencies. Total of 20

words were compared for each speaker for framing valuable and precise opinion. The

intraspeaker variation was also studied to determine the amount of natural variation in a

person’s speech and the frequency range in which he or she can speak.

RESULTS

The auditory analysis of both questioned and control recording and subsequent acoustic

analysis by using Computerized Speech Lab. (CSL 4500) revealed that voice of the speaker in

questioned file matches with the known sample of the suspect in respect of their acoustic cues

and other linguistic and phonetic features. Hence, it was opined that the voice in questioned and

control sample were of the same person with highly probable identity. The results of

spectrographic comparison of the voice of the suspect are shown in figure 1 to 10.


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The culprit was awarded with death sentence on the basis of his voiceprint obtained from

the mobile phone recordings of the victim’s father (figure 11).

CONCLUSION

In lieu of the above discussion, it can be inferred that the analysis and comparison of

voice evidences is quite complicated but absolutely possible. The skill of an examiner itself

along with chosen parameters and selection of appropriate technique for identification is largely

decisive and can facilitate accurate and conclusive results. There have been many advancements

and success made in this field, however, much remains to be done in order to overpower the

daunting limitations which still prevails and limits the process. If we successfully overcome all

such limitations, this technique with its promising features will have an obvious advantage over

the pre-existing ones for establishing individual.


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ACKNOWLEDGEMENT

We gratefully acknowledge our debt to Sh. S. G. Khandelwal, Deputy Director, FSL

Ahmedabad, Sh. K. J. Golania & Sh. D. G. Shah, Scientific officers, DFS, Gandhinagar, for

sharing their expertise, providing selfless support and supplying valuable inputs at each and

every step of our work.

REFERENCES

1 Decker JF, Handler J. Voiceprint identification evidence- out of the Frye pan and into

admissibility. The American university law review

www.wcl.american.edu/journal/lawrev/26/decker.pdf

2 Moenssens AA. Admissibility of Scientific Evidence - An alternative to the Frye rule.

William and Mary law review. Volume 25, issue 4.

3 Gfroerer S. Auditory-instrumental forensic speaker recognition. Eurospeech, Geneva, 2003

4 Campbell JP. Speaker recognition: A tutorial. Proceeding of the IEEE, 85:1437–1462,

September 1997

5 French P. An overview of forensic phonetics with particular reference to speaker

identification. Forensic linguistics, 1(2): 169-181. 1994

6 Majewski W, Basztura C. Integrated approach to speaker recognition in forensic

applications. Forensic linguistics, 3(1): 50-64. 1996

7 Samudravijaya K. Speech and speaker recognition: a tutorial. Tata institute of

fundamental research, Mumbai

8 Sharma BR. Scientific criminal investigation. universal law publishing company

9 Broeders APA. Forensic speech and audio analysis forensic linguistics. 13th Interpol

forensic science symposium, France, October 16-19 2001

Documents

Journal of International - JIARMsimilarities or differences of patterns of the energy, frequency and amplitude distribution of the voice sample. For performing the spectrographic analysis