Source: Rom J Leg Med (2025) 33: 183–189; DOI: 10.4323/rjlm.2025.183
By Kristina Baumjohann, Mark Benecke
Abstract: A homeless man died during an attack by two other men due to three fatal chest stab wounds. The single and double-edged knives resp. their blade lengths did not correspond to the stitch channel depths. These channels had both pointed and blunt wound angles.
We were commissioned to investigate whether the dimensions of a stabbing channel allow conclusions to be drawn about the dimensions of the tool causing the stabbing and whether conclusions can be drawn about the number of cutting edges of the stabbing tool on the basis of a stitch channel. We carried out our investigations on the basis of a detailed summary of the known sources.
Keywords: stab wound, forensic biology, knives, wound angles.
CASE DESCRIPTION
According to police reports, two men attacked a homeless man, each with a knife. As a result, the victim suffered several stab wounds to his body; three chest stab wounds were fatal for him.
During a police search of the apartment, the murder knives were found in the kitchen sink of one of the attackers. The men’s legal representation asked us whether these knives could have caused the wounds to the victim, as the blade lengths of the knives did not appear to correspond to the stab insertions depths (Table 1), and the chest insertions had pointed and blunted wound angles. This would serve to classify the forensic findings. As we also work forensically with bloodstains, we agreed to provide an expert opinion [1-3].
The knives, described in the file as daggers, were described as follows:
- Dagger 1: 9.5 cm inside length, handle length 8 cm, blade sharpened on both sides (double-edged)
- Dagger 2: 9.5 cm inside length, handle length 8 cm, serrated blade and back of the knife (single-edged).
No information on the width of the knife blades was found in the files, but a blade width of approx. 1.2 cm could be estimated from blurred photos (Fig. 1). In the following report, we refer to the terms “length”, “width” and “depth” of a stab wound as shown in Fig. 2. For example, the length of a stab wound should not be confused with the depth of the insertion but refers to the length of the incision wound on the surface of the skin or organ.
We should check here in the sense of inclusion/exclusion of the knives found whether: a. the dimensions of a stab insertion allow conclusions to be drawn about the dimensions of the implement that caused it and b. the number of cuts made by the instrument can be deduced from a stab insertion.
As there was no other option for the client to get advice and it was a classic criminal investigation topic, we agreed to work on it.
Definitions of terms and information
Stab wound
In the case of a stab wound, a stab insertion is created by cutting through the tissue with a pointed or tapered implement that is mainly guided vertically to the surface of the body [6].
Cutting injury
In the case of a cutting injury, sharp longitudinal tissue cuts are created where an implement is guided parallel and/or tangential to the surface of the body [6].
Cleavage lines/Langer’s lines
Langer’s cleavage lines were described in 1861 by the Austrian anatomist Karl Langer with reference to an observation by the physician Guillaume Dupuytren; they are therefore also known as Langer’s lines. They correspond to the natural alignment of the collagen fibers (elastic fibers) of the dermis (dermis, located directly under the epidermis) [7]. Their arrangement in individual skin areas varies; they run in the direction of the least elasticity of the skin (Fig. 3).
The shape of the stabbing implement in the skin/organ created at the moment of impact can be changed by skin tension and the direction of the cleavage lines (Fig. 4). Injuries in the direction of the cleavage lines are less gaping, as the skin is stabbed in parallel to the elastic fibers. If these fibers are cut crosswise, however, a gaping wound occurs [6]. A gaping, slit-shaped skin incision can also be caused by a circular stabbing implement owing to the dependence of the wound shape on the position of the incision in relation to the cleavage lines [5, 7].
Byard et al. (2005) describe two cases in this regard [10]: In case 1, owing to the rectangular shape of the wound, a rectangular or square tool is initially assumed to be the cause of the wounds (Fig. 5). As the skin tension ceased after death, the stab wounds changed during the autopsy and resembled “typical” knife wounds (Fig. 5). In case 2, circular defects turn into slit-like defects due to skin tension (Fig. 6).
Triangular and square objects, on the other hand, tend to leave characteristic, i.e. triangular or square, wounds (Figs. 7, 8) [7].
Reconstructions and classifications to objects
The classification of an implement used to cause an injury is difficult and sometimes not clearly feasible. It is therefore wrong to assume that stabbing implements without a cutting or sharp edge leave cross-sectional wound openings on the skin or organs. Circular tools, for example, do not necessarily leave circular injury patterns: A circular instrument can leave a slit-shaped opening in the skin that is initially indistinguishable from a knife wound (compare cases of [10]). The shape, length and width of the skin slit are based on the cleavability of the skin cut and thus on the alignment of the Langer’s lines (see also Figs. 3, 4) [9].
Reconstruction of the implement’s shape based on the wound
Wound angles are often characteristically shaped (Fig. 9): Single-edged, incisal wound angles are pointed. Knives with a rounded, angular or V-shaped back often leave a bifurcated (forked) wound angle (Figs. 7, 8, 10) [5].
However, this kind of bifurcated wound angle on the side of the implement’s cutting edge can also be caused by an (even slight) change in the blade axis during insertion, as the knife has changed its position as it is removed. This means that in these cases it is no longer possible to deduce the shape of the instrument from the stab wound or the angle of the wound [5, 6] (Figs. 10, 11). If a knife is used to make several piercings one after another, the same knife may leave first a stab and then a cut in the skin. The overall appearance of the wound can vary and depends on the course of the Langer’s lines.
Sometimes it is even difficult to tell whether the stab wounds were suicidal or caused by another person [14]. The shape of a stab wound may allow conclusions to be drawn as to whether the knife had one or two cutting edges (Fig. 12). However, if this cannot be clearly determined from the stab insertion and the injury, this does not mean that the knife was not double-edged or single-edged [7].
Single-edged knives with sharp back edges that are not cutting edges can cause wounds that are indistinguishable from wounds caused by multi-edged stabbing implements [9].
A wide knife back leaves a square or blunt wound angle due to its wider “cutting” side and an acute angle through the actual cutting side (Figs. 8, 13). The wide wound angle can tear open in a jagged manner with a very wide knife back. In this kind of case, it is difficult to draw conclusions from the shape of the injury as to the shape of the blade or the stabbing implement (Figs. 10, 14) [7].
If the instrument is rotated or pulled out on a different axis after piercing, it becomes even more difficult to draw conclusions about the shape of the implement; the edges of the wound may be serrated, triangular or wing-like in shape, etc. [7] (Fig. 11). As a rule, knives with a serrated edge or a forked tip rarely leave a clearly identifiable wound shape on the skin. If the insertion line runs along a bone, for example, this can result in conspicuous scratch-like abrasions arranged next to each other with similar spacing [5]. This is illustrated in Fig. 15: Here the knife edge was guided parallel to a rib so that the edge of the knife grazed the rib and the wavy pattern of the knife edge was reproduced on the rib and also in the tissue. The exact shape of the wound angle can often only be determined during the autopsy when the existing skin tension is relieved and joined together by pushing it together [5].
Reconstruction of the blade width based on the length of the incision
The measured length of the incision on the skin or organ surface does not necessarily indicate the width of the knife blade (Fig. 16). The reason for this is that the angle of entry can be diagonally different to the position of the cleavage lines (see above). With fixed knives, for example, the stab wound (the skin incision) is usually longer, but can occasionally appear narrower [9] (Fig. 12).
If the skin is additionally cut when the knife is pulled out of the wound – for example by movements of a body/the bodies and/or the blade during the act of crime – the stab wound is longer than the width of the blade; more precise information can be obtained from the three-dimensional (!) shape of the incision channel (Fig. 2) [6].
If the insertion implement is rotated during the stabbing, this can reduce the length of the incision opening. It can be dovetail-shaped, triangle-shaped, banana- or boomerang-shaped, polygonal, etc, (Figs. 10, 11). These shapes can arise when a horizontal movement sequence is added to a vertical one (Fig. 12) [5].
A tapered blade has different widths between the tip and the handle (Fig 17). If the entire length of the knife is not inserted into the body, the length of the incision channel will not correspond to the maximum width of the knife (Fig. 16) [5].
Reconstruction of the blade length based on the length of the stab insertion
The longitudinal axis of a stab wound is often not straight, owing to the movements usually carried out during the execution of the crime. The blade can sever tissue fibers of adjacent muscle groups in a contracted state: The tissue gapes apart. During the autopsy, however, the formerly contracted fibers are relaxed; the wound channel is interrupted by intact tissue layers or is interrupted in its longitudinal axis [5].
The ability of the skin to return (so-called retractability) to its normal state of tension (= resting state) must also be taken into account: If a knife is pulled out of a wound, the stab insertion can be a few millimeters shorter than the knife blade. The retraction is again dependent on the position of the incision in relation to the Langer’s lines and the elasticity of the tissue.
If the victim is stabbed with great force, the stab insertion can be longer than the length of the blade of the instrument used to commit the crime, as the tissue is pressed in and deformed by the forceful and rapid stabbing [5, 6, 8] (Fig. 18). This applies in particular to stabs in the abdominal area [5, 7]. It must also be taken into account that the knife is not always pushed in all the way to the handle [5, 7]. In this case, the stab insertion appears shortened compared to the examined blade.
The stab insertion can also appear angled if the muscles and connective tissue shift during the stabbing; sometimes the end of the stab insertion can no longer be determined [7].
Since stab insertions are measured during autopsy on bodies in a straight, stretched, relaxed and motionless position, they may not be comparable to the body position during a crime. However, statements about the course of the stabbing in soft tissue (from top to bottom, from bottom to top, etc.) depend on the posture of the victim and perpetrator at the time of the stabbing [7]. Stabs from top to bottom are often found mainly on the head, shoulders, upper body or thighs; stabs from bottom to top, on the other hand, are found in the abdominal and groin region [5].
CONCLUSION
Can conclusions be drawn about the dimensions of a dagger from the dimensions of a stab insertion?
It is sometimes possible to deduce the number of blades (here: sharpened on one or both sides) of a knife from the shape of the stab wound. However, if the stab insertion and injuries are not sufficiently distinct, it is not possible to determine whether the knife was double-edged or single-edged. Sometimes there are also three blades [11].
There are many factors that influence the dimensions (length, width, depth) of a stab insertion. These factors include the course of the cleavage lines at the incision site, the shape of the implement, a change in the blade axis during stabbing, movements of the bodies of the victim and/or perpetrator, multiple (stabbing) in one place, the combination of stabbing and cutting during the execution of the stab, the state of tension and relaxation of the skin/tissue while alive and dead, and the ability of the skin to be compressed and relax (ability to retract).
Wounds caused by single-edged knives with sharp back edges (which are not cutting edges) can resemble stabs from multi-edged stabbing implements too closely. It is then impossible to tell which implement with how many blades caused the stab wound.
Conflict of interest
The authors declare that they have no conflict of interest.
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