Medico legal questions involving a firearm crime
Is the injury caused by discharge of firearm?
Firearm wounds are recognized by the appearance of clothing and body entrance and exit wounds, the track of the bullet, and the presence of bullet or pellets and residual matter in the clothing or around entrance wound and in the tissues.
What kind of weapon fired the shot?
The kind of firearm can be determined by the size, shape and composition of the bullet, and examination of cartridge, shots and wad left in the body or found at the scene of the crime and the appearances of wounds. With the shotgun, the appearances of the wound are characteristic.
In muzzle-loading gun, the wad consists of plug of paper or cloth; in breech-loading gun of circular discs of felt or cardboard, from which the bore of the gun can be determined. Stains on the clothes or skin may show whether black or smokeless powder was used, and microscopic and chemical examination of the stain is helpful in finding out the particular brand of powder.
Evidence of recent fire can be made out for a few days, by examination of the weapon for mercury vapor. Spent cartridge contains residues of primer and detonator.
In firearm examination, the primary principles of identification are
- determination of caliber and type
- number of rifling grooves
- width of rifling grooves
- direction (left twist or right twist) of rifling grooves
- pitch (angle of the spiral) of rifling
These are used to determine whether a bullet could have been fired in a type or model of a gun or specific weapon. The bullets expand into the grooves in the rifling, sealing the barrel and prevent excess escape of gases ahead of the bullet. The firearms leave their signature on the cartridge case and on the bullet.
With all rifled firearms, the bullet is slightly larger than the barrel, and as it passes through the barrel, its sides are marked by the rifling of the barrel (primary markings; class characteristics) and cause the bullet to rotate. Class characteristics (bar codes) are determined before manufacture of the gun and result from manufacturing specifications, design and dimensions.
The class characteristics in fired bullet identifications would be
- number of lands and grooves
- direction of twist of the rifling
- rate of the twist of the rifling
- width of the lands and grooves
They are most useful in identifying the make and model of gun involved. The surface of the bullet is also grooved by irregularities on the inner surface of the barrel itself (secondary markings; individual or accidental characteristics), which are specific for that particular weapon. These irregularities are produced by the sticking of the particles of the bullet to the bore when shots are fired and is known as ‘metallic fouling’.
Individual characteristics also result accidentally during manufacturing process, are usually microscopic in nature, and have random distribution. They are useful to identify one specific gun to the exclusion of all others “bullet fingerprinting”.
Sometimes, lead bullets may carry weave pattern of cloth. The bullet found in the body known as crime bullet or exhibit bullet is compared under a comparison microscope, with one fired from the suspected weapon known as test bullet.
The suspected weapon is fired, using the same brand and type of ammunition into a box filled with cotton waste (bullet traps), a bag of rags, a sand bag, oiled saw-dust, blocks of ice, water tanks (bullet recovery tank) or against white blotting paper.
Fresh pork skins, cleanly shaven are ideal for comparison with patterns on human skin. From the fired cartridge case, the caliber and type of cartridge and its manufacturer can be determined, from the shape and size of the case and the stampings on the case head.
Fired cartridge cases also may be identified with the firearm from which they were discharged by a study of the marks left on them by the weapon. They are:
- The firing imparts its general shape, size and tooling imperfections, striking the primer in centrefire cartridges, or case rim in rim fire cartridge.
- The internal pressure of firing, forces the soft brass head of the cartridge case against the breech face, which produces markings.
- The extractor usually marks the rim of a cartridge case while withdrawing the cartridge from the chamber, but may also make marks as it slips over and engages the cartridge rim or at the time of disengaging the rim. The end of the extractor hook may produce. markings against the case wall next to the head.
- The ejector strikes the rim or head of cartridge sharply during ejection and usually leaves a mark.
- The magazine or clip may leave both class and individual markings. Lips of a magazine usually mark the rim edges of cartridges as they are stripped from it and chambered.
- Imperfections at the edge or mouth of the chamber will also mark the cartridge case as it is moved into and out of the chamber in loading and extraction.
From what distance and direction was the shot fired?
The range of fire is determined by the presence or absence of the marks of smoke, flame, tattooing, etc., on or in the body of the victim. When the range is greater, it can be determined only approximately and with difficulty, from the nature of wounds and penetration. Test fire with suspect weapon using the same ammunition is useful for estimating the range.
The direction of the track depends upon the posture of the body at the time of impact. The direction of fire may be determined from the position of entrance and exit wounds and the track, bearing in mind the possibility of deflection of bullet and the different relationships of the parts of the body in movement.
Sections of the skin and subcutaneous tissues taken from trans-cutaneous portions of bullet wound may provide evidence as to direction and range of fire. Carbonisation, desiccation or recognition of particles of debris embedded in epidermis near the bullet hole may indicate close range of fire and may distinguish entrance and exit sites.
The findings of debris along the track and in laceration adjacent to it suggest fire at contact range. The range from which the weapon was fired can be estimated by lead deposits around the entry wound. Swelling and homogenization of dermal collagen caused by heat of bullet, is more marked at the entrance than the exit site.
If multiple wounds of entrance and exit are present, could they have been produced by a single bullet?
This has been already described.
If multiple wounds are present, were they produced from the same or different weapons?
This is determined by examination of the wound and of the bullet, cartridge, shots, wad, etc.
When was the firearm discharged?
Tissue reaction to firearm injury is similar as for other types of injury. If black powder has been used, hydrogen sulphide may persist in the barrel for a few hours if breech is closed. The washing from barrels having discharged gunpowder are alkaline, contain nitrite, sulphate and thiosulphate. Smokeless powder leaves a dark grey deposit in the barrel of a recently discharged firearm. It forms a neutral solution with distilled water and contains nitrites and nitrates, but no sulphides.
The mixture of gases of explosion has a peculiar smell, which can be noticed prominently up to 4 to 6 hours. After 24 hours no smell is experienced after the discharge of a gun. Due to backward escape of gases from a fired weapon, the hand of the person will receive gases which carry particles of unburnt powder.
(i) PARAFFIN TEST OR DERMAL NITRATE TEST
It detects gun powder residue (nitrates and nitrites). Melted paraffin is brushed on the surface of the hand. The wax is removed and inner surface of wax cast is treated with diphenylamine or diphenylhenzidine reagent. A blue color develops where residue is present. It is obsolete.
(ii) HARRISON AND GILROY TEST
This test is not specific for firearm discharge residues, but only for certain elements or compounds to be found in such residues. This detects the presence of antimony, barium and lead. A cotton swab moistened with molar hydrochloric acid is used.
(iii) Neutron Activation Analysis
This chemical method is useful in identifying minute traces of elements present in the hair, nails, soil, glass pieces, paints, gunshot residues, drugs, etc. This is helpful when samples for comparison are available. It is based on the detection and measurement of characteristic radioisotopes formed by irradiation in a nuclear reactor. The atoms of the elements present in a specimen are bombarded with neutrons.
Some of the nuclei of the atoms capture neutrons. Those atoms capturing neutrons become radioactive. The radioactivity is measured with a detector connected to an analyzer. In firearm discharges, the residue from the suspect’s hand is removed for testing either by the ordinary paraffin cast or simply by swabbing the back of the hand with cotton-tipped swabs, moistened with 5% nitric acid.
Ideally four cotton swabs should be used to swab both palms and the back of each hand, a fifth swab should be sent separately as a control. As gunshot residue comes out of the barrel, it is the hand that was used to hold the barrel and the one upon the trigger that is likely to give a positive result. Antimony, and copper from the primer are the components of residue which are detected.
(IV) ATOMIC ABSORPTION SPECTROSCOPY (AAS) AND FLAME LESS ATOMIC ABSORPTION SPECTROSCOPY (FAAS)
They are suitable for measurement of antimony, barium and copper in gunshot residues. This analytical system utilizes high temperatures to vaporize the metallic elements of the primer residues and to detect and quantitate them. NAA and AAS can aid in
- identifying holes in clothing, tissues, wood, etc. as bullet holes, from the presence of lead, antimony, barium and copper,
- determining range of fire from concentration pattern of antimony around the bullet hole,
- determining common origin of bullet fragments of shotgun pellets found at different places, from the concentrations of lead, antimony, arsenic, copper and silver in these alloys,
- determining from the presence of lead, antimony and barium on hands whether or not a person has fired a gun.
(V) SCANNING ELECTRON MICROSCOPE- ENERGY DISPERSIVE X-RAY ANALYSIS (SEM-EDXA)
It is the most sophisticated tool which can detect most minute traces of gunshot residue (GSR) found on the body of suspect. As a gun is fired, the GSR comprising chemical substances that burn and produce gases providing the velocity for the bullet, and metals such as antimony, barium, copper, etc. are also sprayed out and get deposited on the hands, clothes and even on the face of the person. The investigator can conclusively prove if the weapon was used by the suspect with a negligible margin of error.
How long did the victim survive?
It depends on the cause of death, i.e., whether from shock and hemorrhage, injury to a vital organ or septic complications.
How much activity could the victim perform following the injury ?
This varies considerably depending on the site of injury and the organ involved. If the bullet destroys motor area, brain stem or cervical cord or if a gaping laceration of the heart or aorta is produced, the victim becomes immediately incapacitated.
Death is instantaneous if medulla is involved. Sometimes, through-and -through bullet wounds of the brain or heart do not cause immediate disability and the person may be able to carry out voluntary acts. Wounds of the auricles are most rapidly fatal; wounds of the right ventricle come next and the wounds of the left ventricle are the least rapidly fatal.
The amount and rapidity of blood loss will also help to form an opinion about the extent of physical activity that would be possible. In any injury to other parts of the body, the victim may be able to walk about.
Is it a case of homicide, suicide or accident?
In deciding the status of a particular case, all the available information should be obtained, including autopsy findings, the investigation of scene of death and the circumstances of the shooting. Each case will present its own problems.
(A) The position and direction of the wound:
These are very important. For suicide the sites of election are:
- temple (about 60%)
- centre of forehead
- roof of mouth
- midline behind the chin
- left side or front of chest
A suicide using a revolver or pistol, usually shoots himself in the right temple region, the bullet passing almost horizontally or upwards and backwards through the head, and making its exit in the left parietal region.
If the individual is left handed, left temporal region is selected. Occasionally, a right-handed person holds the weapon with the butt projecting backwards and the thumb on the trigger, in which case the direction may be different. Sometimes, the gun is put into the mouth, nose, ear or on the face or undersurface of the chin, and fired upward into the brain.
In some cases, the suicide interposes his hand between the pistol and his head, shooting himself through the palm of the hand. Suicidal wounds of the chest and abdomen are less common.
On the chest, the gun is fired into the cardiac region in a backward direction with a slight deviation upwards or downwards either to the right or left. On the abdomen, the gun is fired into the epigastric region and produces perforations and lacerations of the upper abdominal viscera.
In rifle and shotgun, the butt is usually supported by ground nd the weapon is fired by hand into the head, or the butt is supported against a wall and fired into the chest or abdomen. The person may attach some string or cord to the trigger and tie the loose end to his foot, lie down and discharge the weapon through the roof of his mouth.
He may tie the cord to some firm structure and pull the barrel towards him, thus firing the weapon or he may press the trigger with a stick or some similar object. The presence of blood splashes on the hand which held the gun or the presence of an impression of the trigger or trigger guard on one or more fingers indicates suicide.
In homicide, a great variety of wounds can occur depending upon the circumstances. If there is a scuffle, some of the wounds may be from close range and the bullets may strike the body in various places and at different angles. If the victim runs, most of the entrance wounds will be on the back. If victim rushes at the assailant, the entrance wounds are on front of the body.
If the assailant is in a panic or under strong emotion, a number of shots may miss the target or graze the skin. Wounds about the sides and limbs are suggestive of murder, if accident is excluded, and wounds about the back, and back of head are strongly suggestive of murder.
Premeditated, calculated homicide by shooting can occur in a variety of ways. In gang feuds, the victim may be surprised and shot by enemies at close range into the back of the head and neck, with the bullet tracks parallel or only slightly deviating.
(B) The nature of the entrance wounds
This is very important. A contact wound is possibly suicidal, unless found on a part of the body which is not easily reached by the deceased, e.g., back of the chest or neck. Suicides usually pull the clothes aside to expose the skin before shooting themselves.
Bullets vertically entering fatal parts like heart or head, indicate suicide. Several methods (combined suicides) or several attempts of committing suicide e.g., hanging and shooting indicate suicide. A close or distant shot is rarely suicidal.
(C) The number of wounds
Multiple wounds are usually homicidal especially if they occur on the back or sides of the body or involve different regions of the body or are non-contact shots. Occasionally, multiple suicidal wounds are seen involving a single region like the temple, chest or abdomen or a combination of two different regions. When multiple suicidal wounds are fired serially, the injuries by the first shot do not incapacitate the victim immediately, enabling him to fire other bullets into his body.
A bullet passing through the brain, causes immediate unconsciousness, but if bone is involved without injury to the brain or a large vessel, the person may retain consciousness and power of motion. A bullet passing through the chest or abdominal viscera, in some cases does not incapacitate the victim and he may be able to shoot himself again.
(D) The position of the weapon
In suicide and accident, the weapon is usually found at the scene of the crime; the gun may bear the victims fingerprints. The hand that fired the shot may show evidence of gun smoke, powder deposits and traces of metals. With handguns, the effects of the components of a shot are commonly seen on the thumb, index finger and the area between them. Blood splashes may soil the gun and the hand, if the hand pulling the trigger is close to the wound.
In cases of murder, weapon is usually not found near the victim. If the weapon is strongly grasped in the hand of the victim due to instantaneous rigor, it is a strong presumptive evidence of suicide. In some cases of homicide, the scene may be altered to simulate suicide in order to conceal the crime. The assailant after producing a contact wound on the anterior surface of the body or an accessible part of head, may place the weapon in the hand of the deceased.
In such cases, the thumb is usually found under and not around the gun handle, and the weapon is not tightly grasped. If the gun has been tampered with after shooting, e.g., removing of empty cartridge and substituting of unexploded cartridge, causes confusion. The absence of weapon is not conclusive of murder, for it may be removed by a person passing the place or in some fatal cases, the deceased is able to walk considerable distance, leaving the weapon behind.
When a person commits suicide, he usually has a motive, and he may leave a note or make preparations to kill himself.
(F) The Scene
Photographs of the scene, the body and the gun should be taken. Fingerprints on the weapon, doors, etc., are useful. If the gun is present at the scene, its position in relation to the body, its make, model, caliber, type of action and description of the ammunition should be noted. Any loose bullets found should be collected. If they are embedded in the walls, ceiling or furniture, they should be extracted and retained.
The place in which the body is found, e.g., in a room in his own house, the state of the room, whether showing signs of struggle or not, the condition of the doors and windows whether locked or not, should be noted. If the body is found in the open, a search for footmarks and marks of struggle must be made.
It is very rare for females to commit suicide by shooting, and rare for persons who are not used to firearms.
(H) Disposal of the body
If the body is removed from the place of shooting or if an attempt is made to dispose off the body, commission of crime becomes obvious.
They are comparatively rare, and usually single. Most of the accidents are caused by carelessness or misuse. The technical reasons for accident are:
(a) the construction of the weapon,
(b) the absence of safety device,
(c) the poor quality of the material used.
Accidents occur when loaded weapons are handled carelessly or carried without safety catch, or when the victim slips while examining, loading or cleaning the weapon. The wounds are found on the front of the body, and frequently directed upwards.
Sometimes, the victim is shot unintentionally by a person who is ignorant of firearms or careless in their use. Occasionally, when the police shoot on law breakers, an innocent bystander is struck by bullets.
Hunting accidents may result from
(a) swinging the weapon through the line of hunters,
(b) ricocheting bullets or pellets,
(c) failing to unload the weapon when jumping over ditches, climbing fences or crawling through them,
(d) failing to unload or unlock the weapon when it is carried or laid down.
In case of a discharge caused by falling weapon,
(a) the weapon or its muzzle will be some distance away from the body, and there cannot be a direct contact shot,
(b) the weapon will show signs of force to allow a discharge,
(c) marks will be found on the ground where the weapon dropped.
Faked Firearm Wounds
Firearm wounds are very rarely voluntarily inflicted for the purpose of attributing murder. They involve non-vital parts and are near wounds.
Identification by Flash
It is possible to distinguish features with the help of a discharge from a gun or pistol up to a distance of about 8 metres, but the details of features of clothing cannot be made out. Thus, if the assailant is well-known to the victim, identification is possible.