Metoda krevních skvrn (BPA) je validní forenzní metodou, spadající do metodik biologických stop, využívajících i trigonomické modely. Přes její historický vývoj byla vícekrát propracovaná až do současné formulace v celosvětově uznávané podobě standardního metodického listu. Jde o metodu, která umožňuje analyzovat dynamické a charakterové vlastnosti kapek krve po dopadu na pevnou plochu, kterou může být podlaha, stěny, strop, různé předměty, ale i šaty a eventuálně i tělo. Dle přítomností takovýchto krevních stop je jí možné využít v rekonstrukci trestních činů. Podmínkou jej jejich dobrá čitelnost. V naší práci jsme odzkoušeli validitu uvedené metody na experimentálním modelu s použitím střelné zbraně. Jsou srovnávané hodnoty výpočtu trajektorií délky dopadu, výšky výstřiku a vzdálenosti letu kapek krve ze vzdálenosti 1, 3, 5 a 10 metrů. Vycházelo se přitom ze dvou různých vstupních předpokladů. Prvním je známá hodnota vzdálenosti dopadu a uhel dopadu kapky krve a druhým známá hodnota výšky výstřiku a uhel dopadu kapky krve. Podle trigonomických vzorců byla pak vypočítaná buď vzdálenost dopadu vybrané kapky krve, nebo výška výstřiku vybrané kapky krve a bez možnosti ověření i vzdálenost trajektorie letu kapky krve. Výsledky dokumentují, že uvedená metoda je pro tyto potřeby jen orientační a vypočítané hodnoty se od reálních odchylují se zvětšující se vzdáleností výstřelu. Až na ojedinělé hodnoty jsou vypočítané výsledky vzdálenosti dopadu kapky krve pravidelně nižší než skutečné hodnoty a vypočítané hodnoty výšky výstřiku kapky krve pravidelně vyšší než skutečné hodnoty. Navzdory uvedeným nepřesnostem mají námi získané výsledky jistou výpovědní hodnotu. Jeví se užitečné využívat tuhle metodu při vyšetřování a ověřovaní průběhu jednotlivých činů v kriminalistické a forenzní praxi, jako doplňkový zdroj informací.
Peter Makovický1; Petra Horáková1; Petr Slavík1; František Mošna2; Olga Pokorná2
Authors place of work:
Czech University of Life Sciences; Department of Veterinary Sciences1; Department of Mathematics
Kamýcka 129, 165 21 Prague 6 – Suchdol. Czech Republic.2
Published in the journal:
Soud Lék., 58, 2013, No. 2, p. 20-25
Bloodstain pattern analysis (BPA) is a valid forensic method which belongs to the category of biological methods using trigonomic models. Despite its development through the years, the method has been re-formulated a standard one and globally used, recognized in standard sheets. This method permits exact analysis of the dynamic and characteristic properties of bloodstains after impact on surfaces such as floors, walls, and ceilings, various exterior and interior items, and clothes. It is also possible to determine the characteristics of blood from the outer part of the body. According to the presence of blood and its quantity, it is also possible to use this method for verification of reconstruction of criminal acts, while being tested for its validity with primary conditions of preserved and readable traces of blood. Even though this method is not considered as the major one or the only one information obtained in this way can be used for judicial. In our research, we tested the validity of this method in an experimental model using firearms. We compared measurements of the lengths of trajectory of impact and the height of the blood sprayed upwards from a distance of 1, 3, 5 and 10 meters. The experiment was based on two main presumptions. The first was the knowledge of the value of the distance and the angle of impact of the bloodstain, the second, the ability of the blood to reach a certain height and the angle of its impact. In accordance with trigonometric formulas, both the impact of the selected distance of drops of blood, and the height of the selected bloodstain could be determined without any verification of the flight trajectory and the distance of bloodstains. The results indicate that the method for these requirements differs from the real values, while increasing the measurements with the indicated spot of the shot. Aside from the unique values which were calculated, other results of the impact of the distance of drops of bloodstain were considered of lower value, and the values concerning the height of the bloods stains after the shot higher than real values. In spite of the lack of total accuracy, we recommend using this method widely and more often for investigation and verification of individual acts in criminal and forensic practice.
Based on the assumption of the
individuality of criminal offenses, interpretation of each offense
requires a different approach. Analysis of events allows us to
understand their dynamics and also contributes to understanding the
behaviour of the offender. Analysis of biological traces in the form
of blood spots is a well-known method applicable for
reconstruction and verification of the credibility of events. As
early as in the work of Balthazard et al. (3) we can find
relationships between the structure and shapes of blood spots. Much
later there were works which determined the relationship between the
trajectory of impact of blood drops and their shape (2). Geometry,
which at that time was commonly used in ballistics, was starting to
be applied for determination of the impact of blood stains. Further
interest in this issue led to independent forensic expertise
concerning analysis of blood stains according to their size, shape
and possibly even quantity. An established international commission
defined the terminology for working with bloodstains.
The specific physical properties of
a drop of blood come from the separation of large quantities of
blood drops round shape after impact, and create a classic
pattern. There is a relationship among these images (6) [Figure
1]. As the impact angle of a drop of a blood is reduced,
the pattern created is more oblong, with the exception of the speed
of a flying drop of blood, including impact on various materials
(8). Thus, it is possible to determine the angle of impact of blood
drops (13). Another method, based on trigonometry, enables
determination of the quantitative parameters of the estimated impact
of blood drops, which significantly helps in analyzing a criminal
offense. The calculation uses the image of a right triangle with
a known angle of the impact of blood drops and the angels of the
other sides [Figure 2]. In a right triangle, one arm of each
acute angle is the hypotenuse and the others the ordinates. The
ordinate lying on the shoulder of the acute angle is called adjacent
to this angle, and the other ordinate is opposite that angle (14).
The question, then, is to calculate the length, height and distance,
and the impact of drops of blood according to these results can
verify the credibility and possibly reconstruct a crime. In most
works, including forensic practice, a calculation method is
employed which uses a trigonometry-based line model.
It seems that the long-term
calculations of the world’s leading experts and its institutions
have already been standardized, and the procedures for all
calculations in worldwide scientific literature have already been
written. These experts are applying this information to applied
science with added computer forms using trigonometric models, more
and more often than re-analyzing already analyzed procedures. This is
the trend of writing the work of home authors, even
though it is necessary to add that this
is rather rare work. The same applies to
the use of bloodstain pattern analysis (BPA) in
applied practice, which we consider as used only
minimally. All of this suggests that although the methodology
of BPA is well known from the specialists, it is
not given enough attention for the practical training as
well as for scientific part. In our work we have
verified the validity of these methods in an
experimental model with detailed methodology and
results. We offer these results to the public.
MATERIALS AND METHODS
Characteristics of the experiment
We developed an experimental model [M1]
which replicated a real situation of blood spatter using a gun.
Blood stored in test tubes was used. After shooting the contents of
the test tubes, we analyzed the blood stains using valid forensic
techniques. The values in terms of trigonometry were then calculated
from the proportion of the blood spots. This model was based on
a traditional triangle [Figure 3].
Collection and transportation of the
Beef blood which was diluted with
K2EDTA [Biolatest] in a ratio of 1:9 was put into 10 ml
plastic tubes with a length of 7.4 mm, a diameter of 7 mm
and with 0.1 mm wall thickness. Each was filled with blood to
the very top. The blood was collected in the experimental stables of
the Czech University of Life Sciences. A total of 40 tubes of
blood were used. Each tube had been previously identified and
accurately recorded. The blood collected was stored in a transport
box and then immediately transported to a professional shooting
Upon arrival at the shooting range, the
tubes were stored in a rack with a peak at an altitude of
100.00 cm and subsequently one of the following distances: 1, 3,
5 and 10 meters, always in a plane with a right angle, so
that each tube of blood shot was perpendicular [Photos 1 and 2]. The
floor was covered in advance with a fine film and adjacent
bright paper, which was changed after each shot. The weapon used was
a Russian-made 78 and TOZ 22LR bullets. Gradually, all the forty
tubes were shot from these distances, while after each shot the width
and height of one drop of blood and the distance from the centre of
the bottom frame were measured [Photos 3 and 4]. The data for each
group were logged immediately after measuring. The blood material was
treated within 2 hours after collection from the last blood tube.
Pictures of the experiment were taken with a camera [Olympus ∝
Data processing and evaluation of data
The angle of impact of blood drops was
calculated from the measured data [Figures 4 and 5]. The results were
obtained in models with classical trigonometric formulae. We used the
following alternatives for calculation: One was the known angle of
impact of the blood drops and the other the known distance of impact
of the drops of blood [x], as well as the height of the sprayed blood
drops [y]. In our model, we then calculated the values of x and y,
including the distance of the flight trajectory of the drops of blood
[l] [Figure 6]. The calculated data were compared with the real
values of these data, which were measured on site.
RESULTS AND DISCUSSION
The results show that the values of x
and y in all ten cases, including all the recorded distances of the
missiles, were with some variations, calculated from this model. All
the data which we obtained documented that this method is
approximate. All the detailed measured values are given in the tables
[Tables 1, 2, 3 and 4]. We can demonstrate that the measured values
approximate the real values. Firearms are frequently used murder
weapons, and as an easily handled instrument are also popular for
suicide. In literature there are studies that this effect is also
documented in trends in the use of various types of firearms. The
work of Molina and DiMaio (11) indicates that firearms have been the
most common instrument for murders and suicides over the past few
years. Their efficiency makes them an instrument with fatal
consequences. In our work we used a Russian-made rifle with
a bullet weighing 2.6 grams, gaining an initial velocity of 340
m/second and initial energy 150 J, with a range up to 2 km.
It is a heavy weapon. In scientific literature there remains
more work to be done to compare patterns for analysing the
significance of the origin of blood stains. In his work Liesengang
(10) indicates that the main finding which determines the estimated
origin of blood stains is the angle of impact. Rowe (15) calls
attention to an error in determining the impact of drops of blood,
and in the work of Benecke and Barksdale (5) the possibility of
determining the precise selection of valid traces of blood is
described in specific cases. These methods are commonly used in
forensic practice and forensic medicine. In fact, they are valid
methods which are an important scientifically-based reconstruction of
the offense and may answer a number of questions (12).
Many works are based on the assumption
of the impact of blood drops in a perpendicular straightforward
direction. This model is applicable in our view when the traces of
blood spots are on a wall. However, if there are drops of blood
on the floor, we think that a linear impact model should not be
used, because it ignores the force of gravity. This is also why we
decided to use a different method of calculation. The
calculations were based on the parabola and its trajectory with
a specially modified formula. We will not state the results of
this experiment, because of its inaccuracy with regard to the
original model. Furthermore, the inaccuracy analogically increased
with the distance. At a distance of 10meters, the deviation
reached an inaccuracy of 100% from recorded measurements. At this
time, this method of the linear model is commonly used around the
world. Knock and Davison in their work (9) emphasize the effect of
gravity on a blood drop. Their study was based on the
variability of the results determining the angle of impact of drops.
The work of Wells (16) indicates that the true origin of a drop
of blood is dependent on several factors, including flight dynamics
of drops of blood. On the other hand, there was no ideal pattern
found, because variation is due to the dependence of drag force on
droplet diameter and velocity, which is different for each droplet.
Bloodstain patterns were evaluated by various techniques to
investigate their size, speed and also their formation (7). In the
one perfect experimental work by Behrooz et al. (4), which deals with
the underlying mechanisms of blood disintegration and its subsequent
effect on the area of origin calculations, it was stated that this
was found to be very accurate with a maximum offset of only
In conclusion, we state that we are new
to this field, but we have tried to find conclusions which would be
as accurate using the method described above. The applied experiment
was performed responsibly, and with the intencion of further
application of this method in veterinary medicine with regard to
shooting of animals. On the level of application we came across some
problems. After multiple attempts using the method on different
models we offer you reputable conclusions, and we recommend the use
of this method during investigations and verification
of individual acts in criminal and forensic practice.
We thank Mrs. Kateřina Žáčková for
editorial assistance with this manuscript.
ing. Peter Makovický, PhD.
Czech University of Life Sciences in
Kamýcká 129, 165 21 Prague 6 –
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