Most criminal cases related to tying of knots feature frequently. In such conditions, it becomes necessary for an investigator to be equipped with the knowledge of ‘Knot analysis’ so that significant clues can be extracted from the nature of the knot that has been tied. The preliminary examination involves the identification of Knot type and determination of its chirality. The principles for Knot analysis should be referred to for relative interpretation. Such systematic analysis of Knots obtained from the scene of crime can help deduce the handedness of an individual and type of crime, whether suicide or homicide.

Standard Concepts:

When dealing with the tying material, e.g., rope, cloth, chain, fibre, etc., there are three basic terminologies (knot landmarks) that need to be known, they are:

1. Wend – It is the terminal end of the material (rope) used to tie a knot.
2. Stand – Segment of the material (rope) that isn’t included in the tying of knot is termed as ‘stand’.
3. Bight – Part of the material (rope) included within a knot is termed ‘bight’.

Some commonly observed Knot types are:

1. Overhand knots
2. Overhand loops
3. Overhand slip lops
4. Water knot
5. Figure-eight knot
6. Half knots
7. Half hitches
8. Clove hitches
9. Granny knots
10. Granny bow
11. Reef bow
12. Reef knots (Hercules knot)
13. Prusik knot
14. Bowlines
15. Fisherman knot etc.

Multiple approaches have been formulated to classify the knot types. Classic division of the knots that is used widely is as follows:

1. Stopper knot/knot – It is a tangled mass located anywhere on the tying material with is intact without any support and absence of loop. E.g., Overhand knots, Figure Eight knots.
2. Loop knot/loop – This is a type of knot that possesses loop(s) in its structure. It can be tied to support or free, immovable, or adjustable. Few loop knots also remain intact even when removed from support. E.g., Overhand Knots, Overhand Loops, Overhand Slip Knots, and Overhand Nooses.
3. Hitches – When the knot tied to certain support reduces into a stopper knot on the removal of the point of attachment, such a knot is referred to as a hitch. E.g., Half Hitches, Cow Hitches, Clove Hitches, Prusik Hitches, Girth Hitches, etc.
4. Bend – When two wends of a tying material need to be hooked together, the knot employed for this purpose is termed as a ‘Bend’. It is generally used to wrap parcels, tie shoelaces, etc. E.g., Granny knots, Water knots, Reef knots, Surgeon’s knots.

Topological Knots: Such knots are theoretical which cannot be untied to form a single, long strand due to the absence of wands. They are identified as single-dimensional curve lines contained in three-dimensional space. In such knots, the determination of several crossing points is considered.

Chirality: Most of the knots that can be found in everyday life have their mirror images. Such knots are referred to as ‘Chiral’ knots, while the knots which don’t have complementary mirror image are termed as ‘Achiral’ or ‘Amphichiral’ knots. The mirror images displayed by such knots are known as ‘enantiomers’ or ‘enantiomorphs’. In forensic science, the S/Z nomenclature system is used for outlining composite knots. However, for Granny knots, S/S or Z/Z labelling is used and for Reef knots, S/Z or Z/S differentiation is used. Depending upon the chirality, the labelling of knots varies.

Basic Principles of Forensic Knot analysis:

Behavioral observation of more than 6000 individuals in various groups was carried out by Robert Chisnall, Canada (2010) over an extensive period of 25 years through fundamental informal means and supported by empirical evidence. Subjects were instructed to tie knots and this intrusive behaviour was observed repeatedly. This study eventually derived standard principles and guidelines regarding analysis:

1. Tying behavior is consistent and reproducible.
2. When basic tying tasks are performed, people tend to tie one enantiomer more than the other. It is nearly impossible to reverse knot chirality.
3. In many tiers it has been found that the same enantiomer is produced regardless of the number of available bands, however, few tiers produced one enantiomer due to the availability of single want, and the chirality was reversed with two wands.
4. The switching of wends results in a reversal of chirality.
5. Alterations such as excessively long wends and pre-existing knots help reverse chirality.
6. Exposure to awkward tying positions such as overhead tying causes reversal of chirality.
7. Initiation and termination of a series of half-hitches can reverse chirality.
8. Tying slip loops and bows can reverse chirality.
9. Provision of knowledge of sophisticated knots to a tier doesn’t promise that the tier will tie such knots out of habit.
10. Most people often tie unsophisticated knots.
11. In the general population, S enantiomer was produced more than Z enantiomer.

Significant Inferences:

It has been observed that common people usually tend to tie the simplest form of knots, such as overhead knots and half hitches. Apart from this, though only 5% of people who belong to a certain profession, who have received special training in the sector in which unusual knots need to be tied, do not tend to tie sophisticated knots.

It is also observed that there isn’t a definite correlation between tier handedness and the chirality of knots. Though Sinistrals (right-handed volunteers) are found making S-enantiomers more often, they are also found making Z-type knots in certain situations.

This is also observed with Dextrals (left-handed volunteers). Another remarkable observation is that, regardless of having prior knowledge about tying a sophisticated type of knot, this behaviour isn’t translated while tying. However, few people who have no clue of how to make reef knots, tied it, indicating that people can also tie difficult knots out of self-discovery. Also, the number of wends available for tying knots can provide forensically important evidence as it plays a role in the reversal of chirality.

In hanging cases, it should be noted that fixed type of knot is tied in 64.4% of hanging deaths and sliding type (running) knot to be tied in 21.3% of cases. However, in the rest of the cases knot type cannot be determined due to the removal of ligature. In maximum cases, it can be found that the knot has been placed at the back region of the neck. This is important in determining the mechanism of death as gross inconsistencies with this matter is an indication of a suspicious death.

Differences between homicide and suicide:

Most suicides are associated with hanging and involve partial or complete suspension. It is uncommon in homicides. Slip knots are prevalent in self-tying cases. At the knot location, an inverted ‘V’ mark can be found present predominantly in soft neck tissue. External tying depicts double-neck ligatures with fixed or immovable knots (three to four). However, evidence of single ligature is commonly observed in suicide cases.

Case study:

An FIR was filed in a village about a woman hanging from a bamboo beam of her own house. When the officers acknowledged the report, they drove to the crime scene. In the meantime, the husband (accused) had cut the rope to claim that he was trying to save the victim, thus simulating the crime scene to claim suicidal hanging. The rope was cut into two pieces, one was which was left hanging from the bamboo beam and the other end was found around the victim’s neck.

Autopsy findings:

The autopsy report suggested that the deceased was about a 28-year-old female of average built. One ligature mark was present around her neck. The brain, spinal cord, larynx, trachea, lungs, pericardium, heart, liver, spleen, kidneys were found congested and the uterus was also found empty. There was a deformity at the 3rd and 4th right ribs at the mid-clavicular lining. A deep and transverse ligature mark was present above the thyroid cartilage around the neck. Bruising and abrasion were present on the left side and in front of the neck about the edges of the ligature mark. Superficial mark of the knot was also present on the left side of the neck.

Forensic evidence:

• One deep ligature mark encircling the victim’s neck indicated homicide.
• Nail scratch mark on cheek and neck.
• Eyes and mouth without tongue protrusion were partially open.
• Absence of dribbling saliva.
• No signs of discharge of urine/faecal matter.
• Absence of any support for the victim to climb up to the hanging point.
• Testimony of suspect was dubious; not supportive of suicidal hanging.

Results:

It was found that the accused attempted to simulate the crime scene to make it appear like a suicide. However, based on circumstantial evidences, forensic evidence, and autopsy findings, it was declared that it was a case of homicide and the husband of the deceased (accused) was convicted.

Conclusion:

Careful observation and analysis of Knot obtained from the crime scene is extremely important for the deduction of significant leads. Lack of training and appropriate analytical skills can render the piece of evidence worthless. Thus, identification of knot type, chirality determination, knot position, and condition of Knot should be done carefully and following the standards. The principles of Knot analysis should be considered and the inferences must be drawn accordingly.

References:

1)     R.C. Chisnall (2016), Structural recognition and nomenclature standardization in forensic knot analysis, Sci Justice.

2)     R.C. Chisnall (2010), Basic principles of Forensic knot analysis: A qualitative study of tying behavior, Investigative Sciences Journal, Vol. 2(3).

3)     R.C. Chisnall (2010), Knot Tying habits, Tier Handedness and Experience, Journal of Forensic Sciences, Vol. 55(5).

4)     V. Ambade, S. Meshram, J. Borkar (2014), Ligature Material in hanging deaths: The neglected area in Forensic Examination, Egyptian Journal of Forensic Sciences.

5)     R.C. Chisnall (2020), Distinguishing between Homicide and Suicide knots and ligatures: A comparative analysis of case and survey data, Journal of Forensic Sciences.

6)     R.C. Chisnall (2011), An analysis of more than 100 cases involving knots and ligatures: knot frequencies, consistent tying habits and noteworthy outliers, Australian Journal of Forensic Sciences, Vol. 43(4).

7)     R.C. Chisnall (2016), Analysing knot evidence: associating innate-habits with sophisticated tying tasks, Scandinavian Journal of Forensic Science, Vol. 22(2).

8)    S. Nath, R. Majumder, HK Pratihari (2020), Homicide hanging–a rare case report, Forensic Research & Criminology International Journal, Vol. 8(1).

The post Forensic Knot analysis appeared first on Legal Desire Media and Insights.

Every day, we come across many routine voices in our civilization amongst which, few sounds become memorable due to the peace they bring out or it could be due to their uniqueness that makes them stand out from the rest. However surprisingly, there can also be such sounds that might fall into the circle of audio enigmas in forensic investigation. 

The study of such sounds for either eliciting the identity of a person (speaker recognition) or to determine the loudness of a sound, is termed forensic acoustics. Forensic acoustics is alternatively also referred to as audio forensics. Scientifically put, “It is a field of forensic science that deals with acquisition, analysis, interpretation, and evaluation of sound recordings.” 

Historical Glimpse:

Since the 1960s, forensic examination of audio evidence has been practiced by forensic laboratories. The initiative was taken by the Federal Bureau of Investigation (United States) to investigate such questionable audio recordings. Over the last forty years, audio forensics has grown considerably and has become a government-recognized profession. Earlier, the investigations were carried out on analog signals but it posed many downsides comprising of deteriorated signal stability and quality as well as low capacity. To overcome this, digital recording pronounced its need with time. They provided better outcomes but at the cost of evidence tampering issue. The ability to alter, resave, and manipulate digital bitstream cannot be ruled out. Thus, there existed an underlying need to determine the authenticity of digital recordings received for identification purposes. Multiple approaches are used to establish the authenticity and source of the evidence. 

Why do we need Audio Forensics?

The analytical report generated by the forensic department needs to be submitted as evidence to the courts for legal proceedings. It is only after the court accepts the evidence, that further proceedings based on that audio evidence can be held. There are many instances in which acousticians need to perform an investigation of the sound sources. There are a few examples which are listed below as:

1. To know if there is a confession from a person about any committed offense. 
2. To figure out how many people were present in the given moment when the recording took place. 
3. To determine the loudness of an alarm if it satisfies the threshold value.
4. To identify if the recording consists of the suspect’s voice. 
5. To analyze if the inconvenience offered to civilians from bar music exceeds valid acceptable loudness value. 

In such a manner, there can be various probable scenarios in which forensic acoustics come into action. Therefore, to carry out an investigation, certain techniques for audio track processing need to be enforced to gain valuable intelligence from the tangible audio clip received.

Phases followed in Forensic acoustics:

Audio forensics fundamentally imbibes three paramount procedures, they are; 

1. Acquisition of evidence involving the establishment of audio authenticity. 
2. Processing of the evidence by employing noise cancellation methodologies and improving the quality of evidence.
3. Interpretation of the data which includes, speaker recognition, crime scene reconstruction, audacity determination, etc. 

The steps involved in the acquisition are as follows:

1. Examining the chain of custody – Authenticity of evidence is of prime importance when it comes to court submissions. Thus, when an audio recording is obtained, it is checked on the custody log. If the authenticity of an audio recording is not proved, it becomes inadmissible in the court of law. Thus, only on verification, the evidence can be considered and permitted for further processing. 
2. Establishing the chain of custody – The evidence that needs to be collected should be from an original source. This is ensured by documenting the retrieval process by videography or capturing associated images. If it becomes functionally impossible to establish the chain of custody, a request for original needs to be issued. 
3. Request for original – Generally, the original version of the recording is asked for, which is the first copied recoverable format of the evidential sound. This becomes easier when it is linked to a digital medium. Retrieval of recordings from analog media poses the chances of sound quality degradation and introduction of noise, unlike digital copies. Digital copies are exact duplicates that can also be verified using hash functions. 

The audio authentication methods are broadly classified into two main categories:

1. Container-based authentication: It involves metadata analysis comprising of HASH value determination and matching. 
2. Content-based authentication: This type involves the assessment of actual data content of the audio file in bit format. 

On successful completion of these steps, retrieval methods are followed which include imaging of the original storage file as well as media, then successful transfer to the portable media, and eventually, the analysis takes place. 

Enhancement:

The interference of other distorted sounds in a forensically important audio recording needs to be eliminated. This procedure is referred to as evidence enhancement. One of the dominant reasons for the availability of such diffused audio data is recording relevant conversations by using hidden microphones. Such clandestine technique provides a forum for the recording of environmental noises captured in the background along with the conversation of forensic importance. To get rid of such irrelevant sounds, quality enhancement of the recording needs to be addressed. This is done by improving the signal-to-noise ratio of the forensic image. This processing is done concerning time-domain and frequency-domain to yield a clear and high-quality signal. 

Analytical phase involves:

1. Critical listening for determination of subtle lifts in voice strength and other detectable variances. In speaker identification cases, careful aural examination helps to know the geographical area native to the speaker. This can be concluded by proper listening to the accent of the speaker. This is because the vernacular influence is quite reflective of a person’s tone when he speaks. 
2. Electronic measurements to have a discrete vision of the associated frequencies along with their intensities.
3. Analysis of metadata to gather information about the recording device and other significant entries. 

Analysis procedures primarily comprise of eliminating the “unwanted” background noises to narrow down on a forensically significant piece of audio. Equalizers and noise reduction software are preferred for such purposes. These extraneous voices can be sophistically removed by using a spectrogram that reflects the intensity of various frequencies and detects signal irregularities available in a sample rendering a sorted assessment procedure. 

Digital signal processing is the widely adopted method for the analysis of audio signals from a voice note. So far, automatic speaker recognition techniques such as Mel-Cepstrum coefficients (MFCC) are applied for the identification of the speaker. The analysis of audio recordings is done in certain special departments of forensic science such as the “Tape authentication and Speaker Identification” in Directorate of Forensic Science Laboratories, Maharashtra. 

There are many free softwares as well as licensed versions available for interpretation. Forensically speaking, discrete Fourier transform, Audacity software, and frequency analysis windows have also proved to be a helping hand for assessment purposes. 

Audio Forensic Report: 

It comprises of an introduction about the objective of analysis enveloping the scientific facts, analysis software used for the analysis of the audio evidence, expert’s opinion regarding the conclusions put forth, and a document establishing the credibility of the forensic audio expert.  

Conclusion:

The aural and spectrographic analysis can be done on a variety of cases in Forensics ranging from aircraft accident issues to gunshot examinations. The signal intelligence obtained from audio evidence help verify the questioned situations and are presented in the court of law. However, the possibilities of facing technical and legal challenges in such examinations cannot be ruled out.

References:

1. Audio Forensics: An Accurate, Arguable and Authentic Approach to Understanding Audio Evidence from https://tasanet.com/Knowledge-Center/Articles/ArtMID/477/ArticleID/124/Audio-Forensics-An-Accurate-Arguable-and-Authentic-Approach-to-Understanding-Audio-Evidence
2. Maher R. Lending an Ear in the Courtroom: Forensic Acoustics (2015). Acoustical Society of America. Vol. 11(3).
3. Maher R. Audio Forensic Examination, Authenticity, Enhancement and Interpretation (2009). IEEE Signal Processing Magazine. 1053-5888.
4. Forensic Speech and Audio Analysis. Acoustics Research Institute.
5. Forensic Audio Analysis from https://clarkesaunders.com/other/forensic-audio-analysis
6. Herrera Martinez, M. et al. Speech pattern recognition for forensic acoustic purposes (2014). Tecciencia. Vol. 9(17), 37-44. 
7. Meuwly D. Forensic Speaker Recognition (2009) in Wiley Encyclopedia of Forensic Science.

The post Forensic Acoustics and its Application in Signal Intelligence appeared first on Legal Desire Media and Insights.