London murder rates 'stabilising'. Metropolitan Police. Image source, Met Police. Paramedics tried to save the victim but he died at the scene. Related Topics. Metropolitan Police Service London violence Mitcham. Published 20 May Published 16 April Published 9 May Published 15 May Each 3-s period collected 30, data points. The LabView program plots an amplitude where amplitude is force versus time plot. A typical output is shown in the on-line appendix, p4.
The data was recorded as a. Data analysis was performed using Microsoft Excel. The primary end point of this study was to provide quantitative data for adult males and females through the use of the dynamometer for forces generated through a range of blunt trauma hand actions and stabbing actions.
The dynamometer data was compared against that of a known testing method, i. This data was then used to consider whether the use of the subjective scale commonly used by court witnesses is appropriate to provide evidence to a court. The data was analysed using descriptive and mixed effects linear regression statistics.
The study was funded by internal resources. The investigators had full access to all the data in the study and were responsible for the decision to submit the manuscript. The volunteers were a mixture of male and female with ages ranging between 21 and 52 and with heights and weights representative of a random sample from the Leicester University population.
The body data of the two volunteer cohorts is presented in on-line appendix, page 5. The individuals undertook a total of stabbing experiments which generated 96,, data points for analysis. The individual penetrative force for skin simulant, pork thigh and pork ribs as well as the blunt edge radii, tip radii and blunt edge tip angle for five steak knives and five all-purpose knives of the type used in the volunteer experiments as well as the flat-headed and Phillips-headed screwdrivers and the instrumented knife were investigated.
The data is presented in the on-line appendix, p7. The average for the individual weapon penetrative forces for each simulant was calculated to provide a baseline against which the volunteer generated forces were considered Table 1. Table 2 and Fig. The results show, as would be expected intuitively, that, except for the male participant push button force, males generate more force than females and the forces generated for males and females are greater with their dominant hand. The greatest force generated was during a punch action followed by a slap, a push with two hands, a single-handed push and finally the least with a push button action.
These observations provide comparative blunt trauma actions to consider the stabbing experiments against. For the results generated from the MTS experiments, the average force required for the all-purpose knife to penetrate all three simulants Table 1 was less than that required to push a button with a finger and for the steak knife lay somewhere between pushing a button to a single-handed push. Mean force generated by blunt trauma actions performed by volunteers with their dominant and non-dominant hands.
Figure 3 shows the mean forces generated by the volunteers stabbing the skin simulant, pork leg and pork ribs as hard as they could be using an all-purpose and a steak knife as well as a flat-headed and Phillips-headed screwdriver. The minimal, maximum and standard deviation data is presented in the on-line appendix, p Male participants again generated more force than the females.
The force generated with the dominant hand was greater than the non-dominant hand, with the only exception being for male participants using the steak knife where the force generated by the non-dominant hand was 2 N higher than that of the dominant hand.
The mean forces generated in stabs using the screwdrivers were higher than those of the knives. When compared to the forces generated to the blunt trauma actions, the mean forces lay somewhere between those generated by a push with one hand and a slap. Mean force generated Newtons by males and females with each implement, by dominant and non-dominant hand with the skin simulant, pork thigh and pork ribs.
Unfortunately, during testing with the pork leg, participant 2 broke both available all-purpose knives at the front bolster. This resulted in participant 9 being unable to carry out any tests using the all-purpose knife for pork leg or ribs, and participants 2, 3, 5 and 6 being unable to carry out any tests using the all-purpose knife for pork ribs. This accounts for the lower than expected mean forces.
In the pork testing, as had been encountered with the MTS, some stabs with the screwdrivers did not penetrate the pork as follows; participant 3 for the Phillips screwdriver with the dominant hand for pork, participant 6 for the Phillips screwdriver with both hands for pork leg, participant 8 for flat-headed screwdriver for pork ribs and participant 10 for the flat-headed screwdriver and Phillips screwdriver for both hands for pork leg. Figure 4 shows the mean forces generated by the volunteers stabbing the pork leg and pork ribs using an all-purpose and a steak knife as well as a flat-headed and Phillips-headed screwdriver whilst using their perceived idea of mild, moderate and severe force.
It shows that the volunteers were able to generate stabs with varying levels of force, and that a stepped increase in the force from mild to moderate to severe in the stabbings for both types of stabbing medium pork leg and pork ribs was able to be produced for both hands and both sex.
For mild force for both the steak and all-purpose knives with both hands, males stabbed at a force above the MTS minimal average penetrative force.
Females on the other hand, with both knives, were able to cause penetration with mild force below the minimal average force identified with the MTS.
When compared to the forces generated to the blunt trauma actions, the mean mild forces lay somewhere between those generated by a push button with one finger and push with one hand. Mean force generated Newtons by males and females undertaking mild, moderate and severe force stabbings with each implement, by dominant and non-dominant hand with pork thigh and pork ribs. Representative examples of the results for the statistical analysis are found in the on-line appendix, p Both stabbing experiments identified significant differences in the forces generated between males and females as well as, for all but one of the analysis, dominant versus non-dominant hand experiments.
Significant differences in the forces were seen between knives and screwdrivers. Strength and the biological material into which it was been stabbed was also found to be a significant factor. The only results that were not statistically independent were those with weapon 1. Weapon 1 was a comparison of the results obtained with a flat-headed and Phillips-headed screwdriver. The results show that there was overlap between the forces generated with each weapon and therefore that the force required to stab with these cannot be statistically separated.
The key issue in deciding whether a weapon creates a stab wound during a stabbing attack is whether the threshold force for penetration of the skin with that particular implement is met. From the previous work of Hainsworth et al. Skin is known to provide the most resistance to penetration with muscle and fat being more readily penetrated.
Thus, once the skin is penetrated, assuming that a force continues to be applied, then the weapon will continue to penetrate to a depth dependent upon the length of the weapon. This penetration can be altered by the weapon encountering cartilage or bone.
For a knife to pass through cartilage, it has been reported that this may require N and for the sternum N [ 6 ]. All of these suggested values will be dependent upon the knife used and will differ from knife to knife even when manufactured by a single company [ 12 ].
Our study also identifies the importance of considering the sex of the assailant, their strength and the hand used to inflict the injury. The data presented in our first stabbing experiments showed that for an unrestrained stab by a man, using their dominant hand, the mean peak force generated was approximately N for pork thigh and considerable less for pork rib.
This force is over three times that previously published for skin penetration and in the case of our baseline MTS data, for the all-purpose knife, over 12 times greater than actually required for pork penetration. For the same experiments, female volunteers generated lower forces than the males approximately half the force generated by a male but these forces were still greater than those required for skin penetration. Had we applied a mild, moderate or severe scale to these values then although the volunteers were asked to stab the dynamometer as hard as they could, i.
The volunteers were able to generate a scale of force, i. Thus, based on the results of both experiments, in the case of a wound tract involving skin and organs only, applying a subjective scale of mild to moderate to severe force in an attempt to suggest to a court that one can differentiate degrees of force by simply looking at the resulting wound is inappropriate.
All that can actually be said is that the minimal force required for that particular implement to breach the skin and cause an injury to skin and soft tissue only has been met. If bone is penetrated, then, based on previous published data, it can be justified to suggest that greater force was used to inflict the injury. It is thus not sensible to use the same subjective mild, moderate and severe force scale to apply to both blunt and sharp force trauma, as currently occurs, despite the area of injury over which the force is applied being very different, i.
Sharkey et al. Recently, Bolliger et al. Our results support the use of a sharp wound specific, two-tiered approach to commenting on force would be reasonable, i. Our results support that a proper forensic investigation is required in all cases of stabbing to determine whether or not the tip of the weapon permits penetration and at what minimal force.
If the tip of the weapon causes penetration at a force in excess of that expected for a stab wound in skin, then it is reasonable to suggest, as with penetration of bone, that greater force than expected was required with the implement to cause the injury. Such terminology, supported by scientific testing, may be more appropriate for court use than the current subjective scale. These results have significant implications for the legal presentation of stab forces in court.
Typically, a mild, moderate and severe subjective scale is used to suggest the level of violence during a stabbing attack based on the sole examination of the resulting wound.
The data in this study does not support the use of such subjective scales especially as it could influence the court in its consideration of the case.
We are of the opinion that the force required in any stabbing requires investigation in four areas: the tip radius of the weapon, minimal force required for penetration, the sex of the assailant and whether the force required for penetration is greater than that that can be generated by a person stabbing. This later requirement is unlikely to be made available to an enquiry but can be based upon published data such as illustrated within this paper. The dynamometer we have described in this paper can facilitate such considerations.
Crime in England and Wales: year ending September Office of National Statistics. Towards quantification of the sharpness and penetration ability of kitchen knives used in stabbings. Int J Legal Med 4 — Forensic Sci Int 67 1 — Knight B The dynamics of stab wounds. Forensic Sci 6 3 — Forensic Sci Int 3 — Article Google Scholar. Forensic Sci Int 2—3 — Forensic Sci Int 1 — Appl Ergon 36 3 — J Clin Forensic Med 10 4 — Proceedings of the Institution of Mechanical Engineers.
Google Scholar. The biomechanics of stab wounds. PhD Thesis, Cardiff University Nolan, G Quantification of forces involved in stabbings. PhD Thesis, University of Leicester. Int J Legal Med 6 — Forensic Sci Med Pathol 12 4 — J Sports Sci 26 2 — J Sports Sci 18 6 — Br J Sports Med 39 10 — Download references. You can also search for this author in PubMed Google Scholar.
Professors Hainsworth and Rutty contributed equally to the conception, funding, supervision and design of the work.
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