Ormstad et al (1986 pp. 529-542) examined the types of knives used in homicides in Sweden, and found that in 62% of cases, the knife was picked up at the scene.
They were invariably the sorts of knives that are found around the home, such as carving knives etc. In the remaining cases, either the perpetrator or victim had brought the knife with them as either protection or for aggressive use.
These weapons tended to include domestic kitchen knives, as well as lock knives and such implements as screwdrivers etc.
Karlsson (1998 pp.21-32) found that weapon knives were most likely to be used in homicides (as opposed to suicides) in Sweden (such as bayonets, stilleto knives and daggers), and that suicides were most likely to use kitchen knives or razor blades.
Kitchen knives were used in just under 40% of homicides and a razor blade in less than 1% of cases.
Object | Suicide (%) | Homicide (%) |
Kitchen knife | 33 | 39 |
Razor blade/ razor | 31 | 0 |
Sheath knives/ tool knives | 9 | 29 |
Pocket knife | 6 | 0 |
Glass splinters | 2 | 2 |
Weapon knives | 1 | 7 |
Scissors | 1 | 1 |
Several objects used | 1 | 4 |
Not known | 16 | 18 |
Sharp objects used in sharp force homicide and suicide in the Stockholm area (1983-1993) (Adapted from Karlsson 1998) #
Knives with single cutting edges such as kitchen knives cause wounds that have a clearly pointed edge, with the opposite edge being squared off (‘boat shaped’ defect) or split (often termed a ‘fish tail’).
Hunt (2003) believes this ‘fish tailing’ to be artefactual, and has demonstrated experimentally that these marks can be reproduced by rocking the blade within the wound.
Green (1978 pp.161-163) carried out research into the biomechanics of knife wounding, and found that the ‘ideal’ weapon was a short, thin bladed stiff knife of approximately 7cm long (such as the commonly encountered ‘lock knives’ or small ‘sheaf’ knives) and that larger knives required significantly more force to penetrate skin – their tip were observed to ‘catch’ on clothing. Cheaper domestic ‘kitchen’ knives tended to bend and break on impact.
Pathologists and forensic physicians are often asked whether a knife was serrated or not. Serration markings can sometimes be made out where a knife has been drawn over the skin surface, for example at the termination of the wound. In practice this finding is not at all a constant feature of wounds made by serrated knives – they are usually indistinguishable from wounds caused by other single-edged knives.
Ciallella et al (2002) pp.82-87 report the characteristics of wounds caused by a survival knife – with serrations on the non-cutting edge (that act as a ‘saw’).
It can be seen that when the knife enters the skin at a shallow angle, the saw edge comes into contact with the skin giving rise to excoriated ‘slashes’, and a ‘V’ shape can be made where the knife is partially removed and moved within the wound. This relative movement occurs often in knife attacks which are dynamic, and the victim, attacker and knife may move relative to each other at any stage of the attack, giving rise to difficulties in interpretation and reconstruction of the events leading to the wounds under investigation.
Knives or weapons with 2 sharp edges (‘double edged’ blades) such as bayonets and ceremonial daggers are rarely encountered in UK forensic practice, but show pointed edges on both sides of the wound, or a spindle shaped entry slit tapered at both ends.
Knives with blade guards (usually referred to as hilt guards) can also produce distinctive bruising at one edge of the wound, where the guard has impacted against the skin, particularly where the skin is supported, such as on the chest wall.
Such hilt marks, however, are uncommon, and Hunt and Cowley (1991 pp.107-112) only identified them in 3% of cases. Knife guards are also sometimes in surprising places (ie. on the opposite side of the knife that would have been expected).
Bruising may also be present where the assailant’s fist impacts against the skin during the stabbing.
Wounds caused by other implements such as screwdrivers and chisels may have abraded edges, and ‘Phillips type’ screwdrivers may give rise to wounds that are stellate in outline. However, dull square shaped objects may also result in stellate wounds due to splitting of the skin at the wound edges, so any interpretation of these sorts of wounds must be made with caution.
Ice picks produce wounds that are sometimes mistaken for small calibre gunshot wounds – i.e. rounded defects surrounded by a thin circumferential rim of abrasion.
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