Stab wound analysis in forensics

A stab wound is produced when force is delivered along the long axis of a narrow or pointed object, such as knife, dagger, nail, needle, spear, arrow, screw driver, etc. into the depths of the body. It is deeper than its length and width on skin. This can occur by driving the object into the body, or from the body’s pressing or falling against the object. The most common stabbing instruments are kitchen knives, sheath knives or pen-knives.

They are called penetrating stab wound, when they enter a cavity of body. When the weapon enters the body on one side and comes out from the other side, perforating or through-and-through puncture wounds are produced.

The entry is larger with inverted edges, and the exit is smaller with averted edges, due to tapering of blade. The victim of a fatal penetrating injury may not show signs and symptoms of injury until many hours have passed.

Characteristics

Margins

The edges of effected area are clean-cut. There is usually no abrasion or bruising of the margins, but in full penetration of the blade, abrasion and bruising (hilt mark) may be produced by the hilt-guard (metal piece between the blade and handle) striking the skin. The margins may be abraded and ragged if the cutting edge is blunt.

The mark will be symmetrical, if the knife strikes the skin at right angle. if the knife strikes in a downward angle, the mark will be prominent above the stab wound, and if the knife strikes in an upward angle, the abrasion will be below the stab wound.

In oblique types, a knife striking from the right will have an abrasion on the right side and vice versa. In such cases, the suspected knife should be examined to determine the compatibility of the shape of the abrasion around the stab wound, with the handle of the knife in question.

Length

The length is slightly less than the width of the weapon up to which it has been driven in, because of stretching of the skin. For measuring the length of stab wound, the edges should be brought together.

Deliberate lateral, forward, or backward movement of the weapon during its withdrawal from the body tends to widen the wound, and the length will be more than the maximum width of the blade. If the instrument is thrust in, and is then completely withdrawn with the cutting edge dragging against one end, it would be extended superficially, producing a tail.

Width

By examining multiple stab wound in the body, the length and width of the knife blade can be determined approximately. The maximum possible width of the knife blade can be approximately determined if the edges of a gaping wound are brought together. Elasticity or laxness of the skin can change the width by one to two millimeters.

A stab wound inflicted when the skin is stretched will be long and thin, which becomes shorter and broader when the skin is relaxed. The opening may be enlarged by backward, forward or a lateral movement of the weapon.

Depth

The depth (length of track) is greater than the width and length of the external injury. It is not safe to find out the depth of a stab wound by introducing a probe, because it may disturb a loose clot and may lead to fatal hemorrhage, or cause serious damage and may produce multiple false tracks.

The depth of it is usually equal to, or less than the length of the blade that was used in producing it, but on yielding surfaces like the anterior abdominal wall, the depth may be greater, because the force of the thrust may press the tissues underneath.

In young persons, the chest is mobile and may be compressed during the stabbing. The breast, buttocks and thigh are indented by a full thrust, and the depth may exceed the length of the weapon. Expansion and retraction of the chest during breathing must also be considered.

Many of the internal organs are not fixed but have a variable degree of mobility. This should be taken into account when estimating the depth. After the withdrawal of the weapon, the wound tends to close by expansion of the tissues along the track. The depth should be determined in the operation theater when it is repaired.

The viscera of a dead body on the autopsy table are not in the same positions, as when the same person was alive and in standing position, or was bent over in a state of emotional tension, at the time of an assault. During fight, fright and flight, the victim may be moving or changing position in a variety of postures, which change by the second.

When tense, the abdomen is usually contracted, and the distance between the abdominal wall and the spine is reduced. When the same body is on the autopsy table, the abdominal wall is relaxed and this distance increases. Similarly, the anatomical relationship between the lungs, liver and other viscera is not the same as when the person is bent at the hips and when lying flat.

In a stab wound on the anterior wall of the chest, the postmortem depth is greater than it was during life, because Of the collapse of the lung. If it is on the back of the chest, the depth will be less, as the lungs will collapse posteriorly.

The force required to inflict stab wound is subjective, and can only be stated in comparative terms, such as slight pressure, moderate force, considerable force, and violent penetration.

stab wound

The depth depends on:

(1) Condition of the knife: The sharpness of the extreme tip of the knife is the most important factor in skin penetration. Once the tip has perforated the skin, the cutting edge is of little importance, and the rest of the blade will pass into the body with ease, without any further force being applied. A thin, slender, double- edged knife will penetrate more deeply than an equally sharp, wide, single-edged blade inserted with the same force. A blunt-pointed instrument requires considerable force to puncture the skin and penetrate the soft tissues.

(2) The resistance offered by the tissues or organs: Apart from bone and calcified cartilage, the skin is most resistant to knife penetration.

(3) Clothing: The amount of clothing and its composition, e.g. multiple layers of tough cloth, leather belts, thick leather jackets, or coats, etc. require greater force.

(4) The speed of thrust of the knife.

(5) Stretched skin is easier to penetrate than lax skin, e.g. chest wall.

(6) When the knife strikes the skin at right angle, it usually penetrates more deeply than when it strikes from some acute angle.

(7) When the knife penetrates the skin rapidly, e.g. if the body falls or runs on to the blade, the momentum of the forward moving body is sufficient to cause fatal injury. However, the knife must be sharp-pointed and held firmly so as to penetrate easily, as a blunt knife held loosely will be turned aside by the approaching body.

A piece of pliable tubing may be introduced gently, and if it goes in easily may reveal the true track. Later, the tubing can be made more rigid and straight by inserting a probe into it. Dissection in the tissues parallel to, but away from the wound, will reveal the track. Radio-opaque material or dyes can be injected into stab wound to demonstrate the track by X-rays.

Shape

The size and shape of a stab wound in the skin is dependent on the type of implement, cutting surface, sharpness, width and shape of the weapon, the direction of thrust, the movement of the blade, cleavage direction, the movement of the person stabbed, and the condition of tension or relaxation of the skin.

Stab wound and incised ones are slit-shaped with two acute angles, or gape open depending on their location and their orientation, with regard to the so- called cleavage lines of Langer. The pattern of fiber arrangement of the dense felt-work of intimately intermingled dermal collagen and elastic fibers is called the cleavage direction or lines of cleavage of the skin, and their linear representation on the skin are called Langers lines, which is almost same in all persons.

Cleavage lines in the dermal layers of skin are mostly arranged in parallel rows. In the extremities they tend to run longitudinally; in the neck and trunk circumferential. The one which runs parallel to the cleavage lines will remain slit-shaped and narrow and the dimensions of the blade will be represented with considerable accuracy.

A stab wound which cuts through the cleavage lines transversely will gape. If the knife is inserted in an oblique plane, the skin defect is wider and the wound may gape asymmetrically and assume a semicircular or crescentic shape.

To ascertain the shape of the instrument, the edges may be manually approximated with slight twisting or they may be held together with a transparent adhesive tape. The resulting slit is considerably longer than the original oval-shaped wound.

This will counter the claim of the defense that the suggested knife could not have produced a stab of the type as seen before reconstruction. The dimensions of the gaping wound are not useful to assess the shape of the blade.

The shape of it usually corresponds to the weapon used, but the shape made by the same weapon may differ on different parts of the body.

If a single-edged weapon is used, the surface wound will be triangular or wedge- shaped, and one angle will be sharp, the other rounded, blunt or squared off. Blunt end of the wound niay have small splits (often in two places) in the skin, so-called “fishtailing”, if the back edge of the blade is stout. Some stab wound caused by single-edged weapon have bilateral pointed ends like those due to double-edged weapons. This is due to:

  • The initial penetration by the knife point to a depth of about one cm., first produces a dermal defect with sharp angles at each end. . As the knife penetrates more deeply, the end in contact with the cutting edge of the blade continues to be sharply angulated. The opposite end which is in contact with non-cutting surface of the knife, also remains sharply angulated because the dull surface does not imprint its shape to the skin defect. It merely causes further separation of the skin which continues to be torn along the course of its original direction.
  • The knife penetrating the skin at an oblique angle. As the knife perforates, it is pulled down with the cutting- edge cutting through the skin, and the blunt surface of the back of the knife does not impart its shape to the skin defect, as it does not contact it.
  • Many single- edged knives have a cutting edge on both sides at the tip.

The initial thrust into the skin will produce a double-pointed stab wound, and as the blade passes through the skin, if it is pulled down slightly, the blunt back portion of the knife will not come in contact with the skin.

The serosal planes and muscle fasciae (pleural surface, liver capsule and the pericardial sac) often clearly show the wedge-like shape of a knife. In some single-edged knives, both ends are blunt.

This is caused if the knife penetrates to full length up to the guard, because of ricasso (short, un-sharpened section of blade between the cutting edge and guard). By examination of a single wound, it is not possible to say, whether it was caused by a single-edged or double-edged weapon. If multiple stabs are produced by a single- edged weapon, examination of all the stab wounds will reveal the single-edged nature of the weapon.

If a double-edged weapon is used, the wound will be elliptical or slit-like and both angles will be sharp, or pointed. If the knife penetrates to full length up to the guard, one or both edges may be blunt because of ricasso.

A round object like the spear may produce a circular stab wound.

A round blunt-pointed object, such as a pointed stick, or metal rod may produce a circular surface wound with inverted ragged and bruised edges. Foreign material, such as dirt, rust or splinters may be found. The blunter the tip of the object, the coarser or more stellate will be the hole it makes.

A pointed square weapon may produce a cross- shaped injury, each of the 4 edges tearing its way through the tissues.

A fall on a pointed article, e.g., pieces of broken glass, will produce it with irregular and bruised margins, and fragments of glass may be found embedded in the soft tissues.

Stab wounds inflicted with a broken bottle, appear as clusters of different sizes, shapes, and depth, with irregular margins, and varying depth.

Stabbing with a fork produces clusters of 2 or 3 wounds depending upon the number of prongs on the fork.

A screwdriver will produce a slit-like stab with squared ends (rectangular) and abraded margins.

 Thick relatively blunt-edged blades, e.g., bayonets, may produce cross-shaped stab wounds, because cutting and tearing of the skin occurs simultaneously and at right angles to each other. When a knife is twisted as it is withdrawn from the tissues, the external one may have a cruciate appearance.

Ice-picks or similar instruments produce it, resembling small caliber bullet wounds.

Irregularly-shaped such as L or V-shaped may be mistaken to be produced by two distinct stabbings in the same location. These atypical injuries are produced by stabbing, followed by simultaneous twisting and cutting (rocking), or the victim moving relative to the knife, or by a combination of the two.

There will be a primary stab wound with an extension of it, due to the knife edge cutting the skin in a different direction as it exits. Small notches in margins of the skin defects or curving can be produced by the same mechanism. A great number of possibilities capable of causing atypically shaped stab wounds exist, the interpretation of which are usually difficult.

If the scissors is closed, the tip of the scissors splits rather than cuts the skin, producing a linear stab wound with abraded margins. Deep penetration will produce ‘Z’-shaped ones. If the screw holding the two blades is projecting, there are small lateral splits in its center. If the two blades of the scissors are separated, each thrust will produce two triangular ones.

A knife with a serrated back edge will produce a stab wound, the back edge of which may be torn or ragged. If the knife enters obliquely, serrated abrasions may be seen on the skin adjacent to the end.

Direction

When the knife penetrates at an angle, the stab wound will have a beveled margin on one side with undermining (undercut) on the other, so that subcutaneous tissue is visible, indicating the direction from which the knife entered.

In solid organs like the liver, the track made by the weapon is better seen. The principal direction should be noted first and other next, e.g., backwards and to the right. If the weapon is partially withdrawn and thrust again in a new direction, two or more punctures are seen in the soft parts with only one external wound.

If it is perforating, it should be described in sequential order: the stab wound of the entrance, the path of the track, and its exit. If it is penetrating, the wound of entrance should be described first, then the depth and direction of wound track.

Example of description of stab wound

Stab wound, wedge-shaped on the right upper chest, placed obliquely, with the inner end lower than the upper outer end. Length was 4 cm. The maximum width at the center was 5 mm. The center was just below the line joining the nipples, being 5 cm. from the mid line, 6 cm. from the right nipple, and 18 cm. below right collar bone.

The inner end was sharp and outer blunt. The lower margin was undermined. A track is formed on the right anterior thoracic wall, passes through the fifth inter-space, through upper lobe of right lung to a depth of 7 cm. A right haemothorax of 400 ml. of fluid and clotted blood is present.

Complications

1) External hemorrhage is slight but there may be marked internal hemorrhage or injuries to internal organs.

2) The wound may get infected due to the foreign material carried into it.

3) Air embolism may occur in a stab wound on the neck which penetrates jugular veins. Air is sucked into the vessels due to the negative pressure.

4) Pneumothorax.

5) Asphyxia due to inhalation of blood.

Concealed Puncture Wounds

These are puncture wounds caused on concealed parts of the body, such as nostrils, fontanella, fornix of the upper eyelids, axilla, vagina, rectum, and nape of the neck. Fatal penetrating injuries can be caused without leaving any readily visible external marks, e.g., thrusting a needle or pin into the brain through the fontanelles, through the inner canthus of the eye, or into the medulla through the nape of the neck. These injuries may not be detected unless searched carefully.

Examination

The following points should be noted :

1) Identification and labeling of cuts and damage to clothing.

2) Distribution of blood stains.

3) Removal of clothing, layer by layer.

4) Identification and labeling of wounds.

5) Wounds:

  • Position (height from heels),
  • location (measurements from fixed anatomical landmarks),
  • description including margins, size, shape, ends, extension,
  • direction,
  • depth,
  • trauma to viscera,
  • estimation of force required,
  • foreign bodies.

To indicate the general character of the instrument which inflicted the stab wound, the term incised’ or ‘lacerated’ should be included in the description of the stab wound, e.g., ‘incised’, ‘lacerated’, etc. The relationship between the wound and weapon can be identified by the shape, width, length, and presence of blood on the weapon.

When multiple stab wound are present, they should be numbered and photographed. A sketch or a printed body diagram should be used.

Incised-stab wound

It is which starts as an incised wound and ends as a stab wound by the sudden thrust of the blade into the body, or starts as a stab and becomes incised as the knife is pulled out of the body at a shallow angle to the skin surface producing an incised.

If a nick or a pork-shaped cut is present at the end opposite to the incised portion, then the wound has started as an incised and ended as a stab. If the fork is at the end of it where the incised arises, then the wound has started as a stab.

The external and internal appearances help to give an opinion upon:

1) dimensions of the weapon,

2) the type of weapon,

3) the taper of the blade,

4) movement of the knife in the wound,

5) the depth of it,

6) the direction of the stab, and

7) the amount of force used.

Examination of the Weapon

The doctor should note :

1) the length, width and thickness of the blade,

2) whether single-edged or double- edged,

3) the degree of taper from tip to hilt,

4) the nature of the back edge in a single-edged weapon, e.g. squared-off, serrated, etc.,

5) the face of the hilt guard adjacent to the blade,

6) any grooving, serration or forking of the blade, and

7) sharpness of the extreme tip of the blade and the cutting edge.

In some cases of stabbing, the blade of the knife may not be bloodstained. In solid organs, bleeding occurs only after the knife is withdrawn, because bleeding is prevented by the pressure of the knife. During the withdrawal of the knife, the muscular and elastic tissue of the solid organs, and the elastic tissue of the skin may contract about the knife, wiping off the blood present on the knife blade.

In such cases, analysis of wiping of the blade might still yield sufficient tissue to perform at least limited DNA analysis and typing. The clothing if present, may also wipe off the blood. An injury may cause deep shock and severe circulatory collapse. Subsequently, even if a deeply penetrating stab wound is produced, there may be little bleeding.

Medico-legal Importance

1) The shape of the stab wound may indicate the class and type of the weapon which may have caused the injury.

2) The depth of the wound will indicate the force of penetration.

3) Direction and dimensions indicate the relative positions of the assailant and the victim.

4) The age of the injury can be determined.

5) Position, number and direction of stab wound may indicate manner of production, i.e., suicide, accident, or homicide.

6) If a broken fragment of weapon is found, it will identify the weapon or will connect an accused person with the crime.

Circumstances of injuries

SUICIDE

Suicidal stab wounds are found over accessible areas of the body. The common site is the chest over the heart region. The direction of the wound is upwards, backwards and to the right. The depth is variable, some are superficial and others enter the pericardium or heart. The suicide may not withdraw the point of the weapon from the skin, and stab himself repeatedly in different directions through the same skin wound. Rarely one stroke is fatal, and the knife may be found sticking in the wound.

In many cases, even multiple stabs do not cause death and the person may resort to other methods which present a puziling picture. To produce impalement on to a knife, there should be enough momentum by the victim moving toward the knife and it would need to be fixed firmly in some way. Stab wounds of the head are rare.

Usually, a number of stabs extending only to the bone are seen in the temporal region. Suicidal stab wounds of the spine, abdomen, neck and extremities are rare. Wounds found on a part of the body usually covered by clothes without corresponding cuts or rents on them are suicidal, as a person who commits suicide exposes his body by opening his clothes and then inflicts wounds. In some suicides, the victim may be able to conceal the weapon.

Common methods of suicide are: poisoning, hanging, burning, drowning, jumping from a height, stabbing and cutting and railway injuries.

HARA-KIRI

It is an unusual type of suicide, in which the victim inflicts a single large wound on the abdomen with a short sword while in a sitting position or falls forward upon a ceremonial sword and pulls out intestines. The sudden evisceration of the internal organs causes a sudden decrease of intra-abdominal pressure and cardiac return, producing sudden cardiac collapse.

HOMICIDE

Most deaths from stab wounds are homicidal, especially if found in an inaccessible area. The wounds are multiple, widely scattered and deeply penetrating, involving the chest and abdomen. lii case of a sudden surprise attack, a single wound is found at a vital spot. If there is a struggle, there may be a number of wounds, sometimes associated with defense cuts on the hands.

In a few cases, a number of wounds may be found in a localized area, almost of the same depth. These occur when the assailant threatens the victim, who is held by another assailant. These wounds are usually seen on the face or neck, and may be far away from the fatal injury. Homicidal stab wounds of the chest may have any direction, but the common direction is at an angle from left to right and from above downwards.

Fatal stab wounds of right chest usually injure right ventricle, aorta or right atrium. Stab wounds of the left chest usually involve the right ventricle when parasternal, and left ventricle as the stab wounds become more lateral and inferior. Severing of the left anterior descending coronary artery is rapidly fatal.

Most stab wounds of the heart and lungs occur over the front of the chest, rarely the sides, and least on the back. Stab wounds of the lower chest can injure the heart and lungs and also abdominal viscera.

Rarely a single stab may produce multiple skin wounds, such as tangential stab of the arm may pass through superficial tissues and then enter the chest wall, or stab through a sagging female breast can pass through the edge and re.enter the thorax.

In OVERKILL HOMICIDE, assailant continues stabbing beyond the victim’s death. When a knife is thrown at a person, the skin resistance will cause significant loss of its kinetic energy and the stab may not be deep because of further resistance of the internal tissues. Postmortem stab wounds do not show bruising and are often yellow, or tan, due to absence of tissue perfusion, parchmented and sharply defined.

ACCIDENT

Accidental wounds are rare. They are caused by falling against projecting sharp objects like glass, nails, etc., or a person may be gored by the horns of a bull, buffalo, etc. An upward or downward track is quite inconsistent with an accidental stab wound.

Impaling injuries are very rare and caused when a person falls or jumps from a building and lands on a fence or ornamental railings at play or mechanical catastrophe at work.

Accidental stab wounds occur if a person is impaled after an accidental fall on to a sharp-pointed object, or by a moving sharp object striking the person. In accidental stabbing, the weapon should be anchored or held firmly.

ACCIDENTAL, SELF-INFLICTED OR INFLICTED BY OTHERS

The following factors are helpful to determine whether the wounds are suicidal, accidental or homicidal.

  • The nature, direction, extent and situation of the wounds.
  • The presence of foreign matter in the wound or adherent to the margins.
  • The nature of the suspected weapon or instrument.
  • Scene of the crime.