Bloodstain Pattern Analysis Laboratory Report

Categories: Science

Analysis, Pages 5 (1078 words)

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Abstract

The experiment conducted in this laboratory report aimed to investigate the various morphologies of bloodstains produced at different angles and drop heights. It sought to determine the effects of drop height on bloodstain diameter, angle of impact, and percentage error. Additionally, the experiment explored how different target surfaces influenced the shape and diameter of bloodstains. The results demonstrated that both drop height and the type of target surface significantly affected bloodstain characteristics.

1. Introduction

Bloodstain pattern analysis (BPA) is a critical forensic technique that involves the examination of bloodstain patterns at crime scenes.

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It relies on principles of physics, including fluid dynamics, to analyze the size, shape, distribution, and location of bloodstains. BPA plays a crucial role in reconstructing events, understanding their nature and sequence, and identifying areas of potential DNA evidence. This analysis integrates knowledge from various fields, including physics, biology, chemistry, and medicine (Brodbeck, 2012).

When blood is released at a 90-degree angle (perpendicular impact), the contact diameter between the blood drop and the target surface increases until it reaches a maximum, a phenomenon known as spreading (Attinger et al.

, 2013). Experimental findings indicate a direct relationship between the height of a blood drop in free fall and the diameter of the resulting stain, with increased drop height leading to larger stains (Attinger et al., 2013). However, as the drop height continues to increase, irregularities such as spines appear along the edges of the stains. Different target surfaces can also influence the characteristics of bloodstains (Attinger et al., 2013).

Oblique impacts result in elliptical-shaped bloodstains, with variations in elongation depending on the impact angle (Adam, 2012).

Previous studies have shown that the ratio of width to length (WL) of an elliptical stain is directly related to the impact angle, expressed as WL = sin(α), providing a method for determining the angle of impact (Attinger et al., 2013).

2. Methods

2.1 Experimental Design

The experiment was divided into two parts: the first part focused on bloodstain diameter at a 90-degree angle, varying drop heights, and different target surfaces. The second part investigated the effect of impact angle (20°, 60°, and 90°) on bloodstain shape and size for two different target surfaces.

2.2 Materials

For the first part of the experiment, Target 1 was tile, Target 2 was carpet, and Target 3 was newspaper. In the second part, Target 1 was paper, and Target 2 was fabric.

2.3 Procedure

In the first part of the experiment:

Each target was labeled with the impact angle (90 degrees) and the drop height (10cm, 20cm, 30cm, 50cm, and 1m).
A portion of brown paper was placed beneath the experiment setup to capture satellite spatters.
The target was placed on the brown paper, and the dropper was positioned at a 90-degree angle using a tape measure as a plumb bob.
The dropper was filled with blood, and air bubbles were expelled from the dropper tip.
A blood drop was released freely onto the target surface for each drop height.
The targets were moved to a safe location to dry, and the stain diameter at its widest point was measured in millimeters.
The point at which further increases in drop height no longer affected stain diameter was determined for each target.

In the second part of the experiment:

Each target was labeled with the impact angle (20°, 60°, and 90°) and a drop height of 50cm.
Target 1 was attached to the angle apparatus, and the dropper was positioned 50cm above the target surface.
The dropper was filled with blood, and air bubbles were removed.
A blood drop was allowed to fall freely onto the target surface, and the process was repeated to obtain two or three measurable stains for each angle.
The target was moved to a secure location for drying.
The width and length of each stain were measured in millimeters.
The angle of impact for each stain was calculated using the formula: sin^-1(width/length).
The percentage error for each stain was calculated using the formula: [(calculated angle - known angle) / known angle] × 100%.

3. Results

3.1 First Part of the Experiment

The results of the first part of the experiment are summarized in Table 1 below:

Target	10 cm	20 cm	30 cm	50 cm	1 m
Tile	15 mm	18 mm	17 mm	18 mm	19 mm
Carpet	7 mm	6 mm	5 mm	4 mm	5 mm
Newspaper	11 mm	12 mm	12 mm	15 mm	16 mm

3.2 Second Part of the Experiment

The results of the second part of the experiment are presented in Table 2 below:

Target	Known angle	Stain width (mm)	Stain length (mm)	Calculated angle of impact	Percentage error
Paper	20°	7 mm	40 mm	10.08°	49.6%
	60°	11 mm	13 mm	57.80°	3.6%
	90°	12 mm	12 mm	90°	0%
Fabric	20°	11 mm	43 mm	14.82°	25.9%
	60°	11 mm	15 mm	47.17°	21.38%
	90°	17 mm	17 mm	90°	0%

4. Discussion

The results of the first part of the experiment confirm the expected relationship between drop height and bloodstain diameter, as observed in previous studies (Attinger et al., 2013). However, an interesting deviation occurred when using carpet as the target, where the stain diameter ceased to increase after 30 centimeters, suggesting that the type of target material can influence stain characteristics.

In the second part of the experiment, the results align with prior research, demonstrating that bloodstains from oblique impacts exhibit elliptical shapes with varying degrees of elongation (Adam, 2012). The calculated angles of impact were generally consistent with the known angles. However, some stains exhibited a percentage error exceeding 5%, indicating potential measurement inaccuracies.

Limitations of the experiment include the use of a dropper, which may lead to variations in blood drop volume, potentially affecting stain size and shape.

5. Conclusion

In conclusion, this experiment revealed that both drop height and target material significantly impact the form and diameter of bloodstains. The relationship between drop height and stain diameter was evident, except in the case of carpet. Additionally, the experiment demonstrated the feasibility of determining the angle of impact by analyzing bloodstain dimensions. However, some measurements exhibited significant percentage errors, highlighting potential challenges in obtaining accurate results in laboratory settings.

6. References

Adam, C. D. (2012). Fundamental studies of bloodstain formation and characteristics. Forensic Science International, 219(1-3), 76-87.

Attinger, D., Moore, C., Donaldson, A., Jafari, A., & Stone, H. A. (2013). Fluid dynamics topics in bloodstain pattern analysis: comparative review and research opportunities. Forensic Science International, 231(1-3), 375-396.

Brodbeck, S. (2012). Introduction to Bloodstain Pattern Analysis. SIAK-Journal - Journal for Police Science and Practice, 2, 51-57. doi:10.7396/IE_2012_2_E.

Karger, B., Rand, S., Fracasso, T., & Pfeiffer, H. (2008). Bloodstain pattern analysis—casework experience. Forensic Science International, 181(1-3), 15-20.

Laan, N., de Bruin, K. G., Slenter, D., Wilhelm, J., Jermy, M., & Bonn, D. (2015). Bloodstain pattern analysis: implementation of a fluid dynamic model for position determination of victims. Scientific Reports, 5(1), 1-8.

Peschel, O., Kunz, S. N., Rothschild, M. A., & Mützel, E. (2011). Blood stain pattern analysis. Forensic Science, Medicine, and Pathology, 7(3), 257-270.