For APRIL 2000 issue

SCIENCE IN CRIME DETECTION

WHAT IS FORENSIC ANALYSIS OF KNOTS?

‑Dr. Anil Aggrawal

We have always strived to provide the readers of Crime and Detective with the latest that is occurring in the field of crime. Keeping with the tradition, this time I am going to tell you something about a new and a very exciting discipline of forensic science – the forensic analysis of knots.

Knots are encountered in criminal situations a number of times. When a man is strangulated, his killer ties a rope or some similar material around his neck, and a knot has to be tied to prevent the rope from loosening. A frequent question in such situations is whether the person could himself have tied the noose. If he could, the case could be that of suicide, but if he couldn’t, then the case would have to be of homicide, and this would go far in solving the crime.

Ropes or other ligature materials such as nylons, belts, wire and clothing, just to mention a few, have been used in the commission of a variety of crimes from Break and Entry to Murder. Although knot analysis is usually confined to death investigations, it can also assist with investigations in other criminal activities. These could be when a robber has tied the hands of a servant to facilitate robbery, or a person tying the hands of a girl in order to rape her. In some cases, people kill themselves accidentally by hanging when masturbating. Such deaths usually come to the doctor as accidental cases of hanging and are termed asphyxiophilia or autoerotism. A proper explanation of this type of death requires a detailed study, and I am not going to take it up here. It has already been taken up in an earlier issue (See Crime and Detective December 1995 issue pages 14-16). Forensic knot analysis is also useful in cases of suicide, where knots are used.

The ligatures in these cases can, in some instances, yield clues to their origin and possible ownership. A comparison of a ligature from a victim or scene could also be physically matched back to a ligature seized from the suspect or his possessions.

Where ligatures have been used, invariably the investigators have noticed knots tied within. The knots located in crime scenes, on victims of crime and in police cases, have been used to bind, restrain, strangulate, hang or gain entry to an area inaccessible otherwise.

Many readers at this stage may ask how an analysis of knots can help in identifying a criminal. It may be stressed here that knot tying is acquired normally by habits and design. Thus a person ties his necktie and scarf by a certain knot. Similarly in different trades we tie various knots in different ways. A surgeon would tie a knot (while tying a suture) in a different way than a sailor. Often the way a knot has been tied would give away the criminal and his trade.

Knot tying is acquired by:-

habit - such as with tying your shoes, neckties, scarves, etc. or,

design - taught specifically by a trade, or learned as a hobby, craft or recreation

Crime scene knots are most often found to:

bind or restrain the victim,

strangle,

or are sometimes located on or near the victim, but not directly associated to the victim.

These knots located at the crime scene are most often done under duress and without planning, so we can therefore draw an inference of the tyer's:

skills in knot tying,

trade or occupation,

hobby, craft or recreation,

chirality in knot tying (not his handedness)

The word chirality may be explained here. This word is often used in chemistry, and is basically a scientific word, but I would like to explain it in as simple terms as possible. Hold both your arms up and look at them. The thumb of the left palm would be facing on the left side, and that of the right palm on the right side. The two palms look similar, but actually they are not. You can’t superimpose one palm over the other. You can join them as in doing a prayer, but that is not superimposition; this is apposition. Proper superimposition means to put them one over the other, so the back of one palm comes in contact with the front of the other. And if you do that, the thumbs would look in different directions. This is due to different chirality of the two palms. Similarly two knots may look the same, but you may not be able to superimpose them one over the other. It is because of different chiralities of the two knots. The word chirality actually comes from Greek root cheir meaning hand. Incidentally this root also gives us several other interesting words such as Cheirology, which is examination of the hand to forecast the future.

After proper collection and preservation of the knotted exhibits, a forensic knot specialist can provide some additional information about the case, which, in the past, has been ignored or not investigated.

(Editor please reproduce figures 001.jpg, 002a.jpg 002b.jpg, 003.jpg here. [Caption: Some types of knots encountered in crime analysis])

More on forensic knot analysis

Simply put, Forensic Knot Analysis is the identification and interpretation of knots and ligatures, in conjunction with other relevant crime scene evidence, which can enable a subjective opinion to be made.

When qualified as an expert by the court, an opinion can be given of the knotted ligatures as they pertain to the crime scene, for example:

Ligatures can be identified to a source in most cases and such identification can reveal information about the ligature, such as:

brand name, manufacturer, model or type

class characteristics (material, lay, size, color)

uses for the ligature (job specific or particular uses in recreation and/or hobbies)

availability / rarity (such as Spectra fibers)

specific clients (BCTel has rope specifically designed and coded for them)

tensile strengths / breaking strengths

physical evidence, such as matching crime scene exhibit to an exhibit from suspect

ligature marks left on the victim can sometimes be matched to a ligature removed from the victim by the suspect

Knots are identified as they exist on the exhibit. However, due to stresses, mis-handling or usage, the original knots in some cases can be capsized to look like a different knot. In such cases the questioned knot (believed the original knot before capsizing) can be identified and explained as to its transformation, as in these cases:

reef knot to lark's head, cow hitch, or bale sling hitch

granny knot to clove hitch or two half hitches

Knots such as the overhand knot and the figure of eight, can be introduced into the exhibit simply by placing a lengthy rope exhibit, as a tangled mess, into an exhibit bag. Here, knots would be identified that were not tied by human hands and would lead to an erroneous conclusion and inaccurate opinion.

Identification of the knots, can provide some profiling of the tyer such as:

knot tying skills

chirality of the knot tied

linkage to job, trade, hobby, craft or recreation of the tyer

designed or intended use of the knot

Identity of the knots can also provide alternate knot names for the same knot. In some instances, very common knots have several alternate names including foreign language names. Knowledge of these alternate names can help the investigator when statements are obtained and a knot is described using a specific name for it. The following are examples of alternate knot names:

reef knot also known as, square knot, Hercules knot, ambulance knot (bandage knot)

overhand knot also known as, thumb knot and half knot

becket bend (or hitch) also known as cat's paw (by loggers, tree toppers)

Who is a forensic knot specialist/expert

"A person who, through experience, has acquired a special or peculiar knowledge of a subject of which he undertakes to testify, and, whether such knowledge has been acquired by study of a scientific work or by practical observation is immaterial."

The expert witness reports fact known, and relevant to the knotted evidence in a particular case. His observations and examination of the knots, ligatures and related crime scene evidence, can result in an opinion as to the significance of these facts.

An expert must be objective and impartial; his evidence should be reliable, clear and relevant. He should keep pace with advances within his field of discipline, and associate or liaise with organizations which help to advance the understanding of this field.

Knot specialist training

He should have an understanding of the historical development of knots, and materials used as ligatures. He should have knowledge of the reference materials available on knots, crime scene techniques, and other related scientific papers on the topic, and how to research the information required. He should have an understanding of the manufacturing process of ropes and other ligature materials. This would entail visiting rope manufacturing plants and observations of the techniques to make these ligature materials. Such knowledge can enhance his abilities to conduct physical matching of ligature exhibits. He should possess the ability to show a demonstrated skill in knot tying techniques, be able to replicate the knots observed or identified in knotted ligatures, and be a practitioner of the discipline.

DESIRED SKILLS

The ability to educate, and communicate his analysis to investigators, medico legal professionals, and the courts, by the preparation of a report of his findings, and/or testimony in court.

The ability to illustrate knotted ligatures, as a means of providing demonstrative evidence to help in explaining his analysis or opinion.

Be able to conduct experiments to prove or disprove a point, such as: "Could the victim have tied himself up?", or "Was a particular knot used, that would have enabled self-release from the ligature?".

By investigating and/or researching knot cases, the specialist can gain practical experience and knowledge.

The ability to author and publish scientific papers on related research done.

Be able to teach or lecture on his knowledge, experience, or work performed within the discipline.

Be able to acquire some computer literacy with respect to using databases, word processors, and drawing programs.

Detection, Collection and preservation of knotted exhibits

Upon the discovery of knotted exhibits at a crime scene, the utmost care and attention must be taken if this evidence is to be analyzed, and information, in the form of an opinion, be obtained. Like any other piece of evidence, care must be taken to protect it from contamination, movement or change, prior to its removal and any movement or change be recorded.

(Editor please insert Pictures insitu1.jpg [caption: Exhibit 'in situ' at scene] and insitu2.jpg [caption: Exhibit after delivery by courier service] here)

At all major crimes, there are a number of services to assist in the investigation, in particular, the Forensic Identification Services, have the responsibility of recording the scene by measurements, photography and in some instances, videography.

After the victim is removed (assuming that there is a murder), then knotted exhibits should be photographed during their removal and examination at the post mortem. This extra step also ensures that any change to the knots from the scene to the analysis, are recorded.

In cases where there is suspected wire used as a ligature, and/or the exhibit has been extensively coated with dirt or mud, or the coating on the wire has been fused by exposure to heat or fire, techniques such as fluoroscopy and X-Rays can be done to reveal the intricacies within the knotted exhibit.

(Editor please reproduce figure tie_vcr.jpg here [Caption: This is one instance where an X-ray of the knots may be useful. In this case the hands are tied at the back. The ligature is wound round the hands in a complicated way, and its intricacies can not be made out easily. An X-ray can help in such cases.]

Editor please also reproduce figure xray_vcr.jpg here [Caption: Xray of tied hands shown in the above picture. The intricacies of the loop can be made out now])

Removal Of Knotted Exhibits

A forensic knot analyst has to keep in mind several things when encountering knots on the scene of crime. You may want to know what are those precautions. The following are guidelines to assist in the proper collection and preservation of the exhibits that contain suspected knots:

(Editor please reproduce figure 004.jpg here. Caption: The noose of a hanging victim should be preserved. This is best done by cutting the noose away from the knot and securing the ends with string or wire. To assure preservation of the knot, it may be necessary to secure it independently.)

1.Never untie a knot.

2.Cut ligatures away from the knots.

3.The cut ends of the ligature should be labeled (e.g. A-a, 1-1) so cut ends can be matched.

4.Tape or string can be used to preserve cut ends from fraying.

5.The knotted exhibit should be laid out and labeled to preserve orientation to the victim.

6.Be careful that loose knots don't fall apart, or that bights and/or crossings not be lost.

7.Where several turns have been used (e.g. around wrists, neck), cut each turn individually and label, then label the group of turns and secure with a string or tape.

8.Don't place lengthy exhibits into a container so that it can become tangled up or knots be introduced into the exhibit.

9.Other forensic examinations required of the exhibit (e.g. Chemistry, DNA, Hair and Fiber) should be done first so that there is no contamination of this trace evidence.

10.If the exhibit is to be examined by the Forensic Laboratory first, the investigator should notify the laboratory personnel that further examinations of the exhibits are to be done and not to disturb the knots contained therein.

******

(Dr. Anil Aggrawal, M.D. is a Professor of Forensic Medicine at the Maulana Azad Medical College, New Delhi. His E-mail is dr_anil@hotmail.com, and his website is http://members.tripod.com/~Prof_Anil_Aggrawal/index.html)