Introduction

When a crime results in bloodshed there is often a vast amount of information that can be obtained from the crime scene in the form of bloodstains. This article aims to give a brief overview of blood spatter analysis and show how it can help reconstruct the crime scene.

What is Bloodstain Pattern Analysis?

Bloodstain Pattern Analysis (BPA) is the examination of the shapes, locations, and distribution patterns of bloodstains, in order to provide an interpretation of the physical events which gave rise to their origin. This is based on the premise that all bloodstains and patterns are characteristic of the forces that created them.

Information that can be obtained from BPA includes the type of weapon used; the number and sequence of blows or gunshots; the direction from which the victim was struck; the position and movements of the victim and assailant; the handedness of the assailant; and the timing of the crime.

Blood Stains Characteristics

Blood spatters can lead to the recreation of a crime because of how blood behaves. Blood leaves the body as a liquid and travels in spherical drops due to surface tension. These drops behave in predictable ways when they strike a surface or a force acts upon them.

There are several different thoughts on how to classify and define bloodstain patterns. One way of categorizing them is based on the mechanism that created the stain. There are three main groups, passive, projected, and transfer/contact.

Passive

Passive bloodstains form due to gravity and can be divided into four types. Passive drops are those created by the force of gravity acting alone; drip patterns result from blood dripping into blood; a flow pattern occurs when there is a change in the shape and direction of a bloodstain due to the influence of gravity or movement of an object. Blood will flow from the body downwards and collect in the lowest areas on or near the injured or deceased person. A pool pattern will form when the source of the blood is stationary for some time.

Figure 1. Passive blood drops (J. Slemko Forensic Consulting 2010)

Transfer

Transfer or contact stains are produced when a surface with wet blood comes into contact with an unstained surface. Transfer stains can be divided into wipe patterns, created when an object moves through an existing stain altering its appearance; and swipe patterns which result as a transfer of blood from a moving source onto an unstained surface. It may be possible to recognise the object that left the pattern, for example, a bloody hand or foot wear.

Figure 2. Transfer Patterns (J. Slemko Forensic Consulting 2010)

Projected

Projected bloodstains occur when a force other than gravity has been applied to a blood source. The force can be internally or externally produced. There are many categories of projected blood spatters, some of which overlap. The two main groups are Impact Spatter and Projection Spatter.

Impact Spatters are created when a blood source receives a blow or force resulting in random dispersion of smaller drops of blood. They typically occur with beatings, stabbings, gunshots or any other circumstance where a foreign object impacts the victim.

Low-velocity impact spatter occurs when an object travelling less than 5 ft/s or 1.5 m/s comes into contact with a blood source. This will result in large spatters between four and eight millimetres. Medium-velocity impact spatter occurs with an object that is travelling between five and100 ft/s or 1.5 and 7.5 m/s. The stain is generally no bigger than four millimetres. This type of spatter can be caused by blunt force trauma or cutting and stabbing actions. High-velocity impact spatter results when the object strikes a blood source faster than 100 ft/s or 30m/s. The stains produced are smaller than one millimetre and have a mist-like appearance. High velocity patterns may be created by gunshots or explosives, but may also be caused by industrial machinery, coughing, or sneezing.

3a) Low-Velocity 

   3b) Medium Velocity

3c) High Velocity

Figures 3 a-c. (J. Slemko Forensic Consulting 2010)

Back spatter is cause by blood directed back towards the source of the force that caused the spatter. This is usually seen in gunshot wounds and the droplets travel in the opposite direction to the path of the bullet. With gunshot wounds there is also forward spatter when the bullet exits the body, the droplets follow the direction of the bullet. In most cases, the back spatter is much smaller than the front spatter because the spatter travels in the direction of the bullet.   

There are three types of Projection Spatters. Arterial gushing/spurting patterns result from blood exiting the body under pressure from a breached artery. Cast-off stains result when blood is released or thrown from a blood-bearing object in motion. Expiratory bloodstains result when blood is blown out of the nose, mouth, or a wound as a result of air pressure and/or air flow which is the propelling force.

4a) Arterial Spurting Stain

4b) Cast-off Pattern

Figures 4 a-b. (J. Slemko Forensic Consulting 2010)

Overlap in classifications

Passive drops can be considered as a type of low velocity spatter, as can arterial spurts and cast-off patterns. Low-velocity spatters can also result from pools of blood around the body of a victim and transfers. 

Target Surface Texture

The type of surface the blood strikes will determine the amount of resulting spatter and the size and appearance of the blood drops.

Blood droplets that strike a hard smooth surface, like a piece of glass, will have little or no distortion around the edge (Figure 5).

Figure 5. (J. Slemko Forensic Consulting 2010)

Blood droplets that strike slightly textured surfaces take on a slightly different appearance. There will be distortion around the edge of the blood droplets (Figure 6).

Figure 6. – Linoleum Flooring(J. Slemko Forensic Consulting 2010)

Surfaces with rough textures, such as wood or concrete will result in distortion to a larger extent and can have spines and secondary spatter present (Figure 7).

Figure 7. (J. Slemko Forensic Consulting 2010)

Reconstruction of the crime scene

In order to reconstruct a crime scene the directionality and impact angle of the blood droplets need to be figured out, so the area of convergence and area of origin can be determined.

Each droplet in a blood spatter strikes the surface from a unique direction and at a unique angle. The impact angle is the acute angle at which the blood drops strike the surface and the directionality is the course the blood droplet followed. When a droplet of blood strikes a surface at a right angle the resulting bloodstain will be circular. When blood strikes a surface at an angle less than 90 degrees the bloodstain will be elongated. The pointed end of the bloodstain will always point in the direction of travel.

Figure 8. Blood Drop Elongation (Freeman S. 2008)

The area of convergence is determined with a two-dimensional representation of the area where lines tracking the pathways of several stains meet, indicating the general location of the blood source in relation to the spatters. At the crime scene, investigators stretch strings from each stain according to the angle of impact; where those strings meet is the area of convergence.

Figure 9. Area of convergence (Wikipedia 2010)

The area of origin is the area in three-dimensional space where the blood source was located at the time of the incident (Wikipedia 2010). It is the area within which the lines tracking both the pathways and the angles of impact of several blood spatters meet. By stretching strings along the angle of impact of each stain, investigators can find the area of origin (Lyle, D.P. 2004).

Figure 10. Area of Convergence and Origin (Freeman, S. 2008)

Interpreting void patterns

A void pattern occurs when there is an absence of blood spatter in an area where normally it would be. Voids can indicate the position of the attacker, as his body would prevent the blood from spattering on surfaces behind him.

Indications from dried or clotted blood

Over time, blood spatters dry. The outer edges dry first. A really dry blood spatter will flake off, leaving a ring around the original diameter of the spatter. The dryness of the blood can help determine when a crime occurred.

Once it has exited the body blood will eventually begin to clot. Clotting can occur within 15 minutes. If some blood spatters are more clotted than others, it can indicate that multiple blows or gunshots occurred over a period of time.

Conclusion: Putting it all together

The blood spatter analyst can reconstruct the scene and determine the exact sequence of events, based on the bloodstain evidence. The analyst would take into account the types of spatter found; the areas of convergence and origin determined from the impact angles and directionality; and the state of the blood whether wet, dry or clotted or some stage in between.

References

• Freeman, S. (2008), “How Bloodstain Pattern Analysis Works”, http://science.howstuffworks.com/bloodstain-pattern-analysis.htm.
• J. Slemko Forensic Consulting (2010), “Bloodstain Pattern Analysis Tutorial”, http://www.bloodspatter.com/BPATutorial.htm.
• Lyle, D.P. (2004), Forensics for Dummies, Indiana: Wiley Publishing, Inc.
• Shepherd, R. (2003), Simpson’s Forensic Science, 12^th edition, London: Hodder Arnold

Bibliography

• Akin, L.L. (2005), “Blood Spatter: Interpretation at crime scenes”, The Forensic Examiner, http://findarticles.com/p/articles/mi_go1613/is_2_14/ai_n29186570/
• Dickerson, M.E. (2010), “Studies in Bloodstain Pattern Analysis”, http://bloody2.com/experiments.aspx 
• Murfin, M. (2009), “Forensic Science of Bloodstain Pattern Analysis: Process of Evaluating Blood Spatter Evidence at a Crime Scene”,  http://crime-scene-processing.suite101.com/article.cfm/forensic_bloodstain_pattern_analysis

For a successful toxicological analysis, samples need to be selected with the desired analytical test in mind and collected carefully. This paper describes the best practice methods for sampling and the effects of post-mortem redistribution on sampling.

Introduction

Sampling is of the utmost importance in forensic toxicology. The reliability and accuracy of any result is usually determined by the nature and integrity of the samples provided. Proper sample selection and collection is important for the results to be accurately interpreted with scientific validity.

The best places to get samples for testing are the locations where chemicals enter the body, concentrate within the body, and along the routes of elimination. Thus blood, stomach contents, and tissues around injection sites may possess high concentrations of the drug. Analyses of liver, brain and other tissues can reveal where a drug or its metabolites accumulated and urine analysis can indicate where the drug and its metabolites are concentrated for final elimination.

Samples from living subjects

Toxicological analysis is usually required on samples from living subjects in cases of drug facilitated crimes or attempted poisonings. In all situations, samples should be collected as quickly as possible and properly labelled. The best containers for liquid samples are disposable hard plastic or glass tubes. When a preservative is needed, sodium fluoride should be used at a concentration of approximately 2% weight by volume. Unless otherwise noted, samples must be maintained at temperatures not greater than 4°C to ensure sample integrity.

Post-mortem Samples

Cases of mysterious deaths tend to require forensic toxicologists to perform extensive toxicological analyses. The availability of autopsy samples in post-mortem toxicology allow for a more flexible approach to the analysis. Some samples have more value than others when specific drugs or poisons are involved in the death.

Autolysis and putrefactive processes that occur after death, as well as post-mortem redistribution, can have a profound effect on drugs and poisons that are present in the body prior to death. For this reason, post-mortem samples should be collected as quickly as possible and in separate containers. For most samples, disposable hard plastic or glass tubes are recommended. Each sample must be labelled appropriately. Samples should be stored at a maximum of 4°C when being analyzed soon after autopsy, otherwise at -20°C.

Samples in Detail

Blood

Blood is the sample of choice for quantifying and interpreting concentrations of drugs and their metabolites. Blood provides a list of toxic substances present in the subject’s body at the time of collection. Concentrations within the blood correlate well with levels of intoxication. A quantity of 10 – 15 ml of blood is required to screen and confirm the presence of most toxic substances.

In post-mortem cases, blood shows what was going on in the body at the time of death. At least two blood specimens should be collected, 30 ml of central blood for qualitative analysis and 10 ml peripheral blood for quantitative analysis.

Urine

Urine is used for comprehensive drug and poison screening. Urine is an easy sample to obtain and is relatively rapid and non-invasive. The accumulation of toxins in urine results in high concentrations that aid their detection. Because the kidneys are situated along one of the body’s major drug and toxin elimination routes, substances can often be found in greater concentrations in urine than in blood.

Urine samples don’t necessarily reflect the toxins the subject was influenced by at the time of the sample collection as it can show substances even several weeks after their ingestion. For example, cannabis can be detected two weeks after use. It can also take as long as 8 hours until a given substance can be detected. This is a disadvantage where death occurs very rapidly after exposure to a drug or poison. In these cases, the urine specimen may be negative for the causative agent. 

A minimum of 30 ml is required for thorough screening in living subjects. In post-mortem cases all urine available should be collected.

Hair

Toxins in the bloodstream can transfer to growing hair and provide an intoxication timeline. Head hair grows at rate of approximately 1 to 1.5 cm a month and so cross sections of the hair at different intervals will give a rough estimate of when the drug was ingested.

Approximately 100-200 mg of hair should be collected from the vertex posterior on the back of the head by cutting as close to the scalp as possible, ensuring that it is clearly marked which end is closest to the scalp and stored at room temperature.

Vitreous Humour

Vitreous humour (VH) is an isolated and protected area of the body. Coupled with its good stability as a biological fluid, these features make this specimen more resistant to putrefactive changes than other post-mortem samples.

The VH and blood maintain equilibrium, meaning that any water soluble chemical in the blood is also in the VH. However substance levels in the VH lag behind levels found in the blood by one to two hours, so testing the VH reflects the concentration of the toxin in the blood one to two hours earlier.

All available vitreous fluid from each eye should be collected separately.

Gastric Contents

Oral ingestion remains the most popular means of exposure to drugs and poisons. Therefore, gastric contents are essential for screening tests. The inspection of gastric contents must be part of every post-mortem examination if possible. It allows the detection of undigested pills or liquids that were ingested just before death. It may also provide qualitative information concerning the nature of the last meal and the presence of abnormal constituents.

All of the available sample should be collected without the addition of a preservative. Undigested pills and tablets should be separated and placed into plastic pillboxes for analysis.

Liver

Since most drugs and poisons are metabolized in the liver, both the parent compound and its metabolites may be present in high concentrations in this tissue, making it a valuable sample in post-mortem cases.

Many drugs can be measured in liver and bile, even when blood tests show no traces of them. The liver may reflect levels of a drug during the hours before death, and the bile may indicate what drugs were in the system during the past three to four days.

Approximately 25-50g of tissue should be collected.

Other possible samples

Other common organs used are the brain, spleen, lungs and kidneys. Nails can be used in a similar way to hair samples. Insects that feed on dead bodies can also be tested for drugs. Collection of scene samples such as drug paraphernalia, cups or bottles, and suspicious household products will aid in a thorough toxicological analysis.

Dealing with post-mortem redistribution

Post-mortem redistribution (PMR) refers to the changes that occur in drug concentrations after death. The drug redistributes into blood from solid organs. PMR is not just limited to blood. The movement of drugs from the gastrointestinal tract into neighbouring tissues has also been shown to contribute to redistribution. PMR is time dependent and occurs via diffusion from a site of high concentration to one of low concentration. Drug properties such as volume of distribution, lipophilicity, and pKa are important factors in PMR.

When post-mortem cardiac blood samples have been compared with samples taken ante-mortem or shortly after death, drug concentrations have been seen to increase up to 10-fold. Femoral blood is also subject to redistribution after death, but less so than cardiac or centrally collected blood.

The anatomical location of blood sampling can influence the drug concentration. The ideal site for sampling is a clamped femoral vein. The liver is also a valuable sample for drugs that undergo PMR. Forensic toxicologists carrying out tests involving drugs likely to undergo PMR must be aware of its potential contribution to the post-mortem drug concentration. Correlation with laboratory data and any available ante-mortem or peri-mortem clinical information is necessary to decipher the cause of death.

Conclusion

The most suitable samples for each forensic case should be taken depending on the type of case. In death investigations two peripheral blood specimens, vitreous humour, a section of liver, stomach contents and a hair sample is recommended. In living subject cases blood, urine and hair is recommended.

The detection of drugs and poisons in post-mortem samples can be more difficult than in clinically derived samples. This is due to the presence of putrefactive compounds and the often-altered nature of specimens in the post-mortem setting.

Toxicologists should take PMR into consideration when choosing the type of samples taken for analysis.

References

• Drummer, O.H. (2007), “Best Practice Toxicology”, Forensic Science International, Volume 169, Supplement 1, 15 June 2007, p. S29.
• Drummer, O.H. & Gerostamoulos, J. (2002), “Postmortem Drug Analysis: Analytical and Toxicological Aspects”, Therapeutic Drug Monitoring, Volume 24, No. 2, pp. 199-209.
• Explore Forensics (2009), “Forensic Toxicology”, http://www.exploreforensics.co.uk/forensic-toxicology.html.
• Lyle, D.P. (2004), Forensics for Dummies, Indiana: Wiley Publishing, Inc.
• Rodda, K.E. & Drummer, O.H. (2006), “The redistribution of selected psychiatric drugs in post-mortem cases”, Forensic Science International, 164, pp. 235-239.
• Shandilya, R. (2008), “Forensic Toxicology”, http://www.buzzle.com/articles/forensic-toxicology.html.
• Tox Wiki (2009), “Recommendations on Sample Collection for Systematic Toxicological Analysis”, http://toxwiki.wikispaces.com/TIAFT+Sample+Collection+Guidelines.
• Yarema, MC. & Becker, C.E. (2005), “Key concepts in postmortem drug redistribution”, Clinical Toxicology, 43(4), pp. 235-241.

Bibliography

• Flanagan, R.J. et al. (2003), “Effect of post-mortem changes on peripheral and central whole blood and tissue clozapine and norclozapine concentrations in the domestic pig (Sus scrofa)”, Forensic Science International, 132, pp. 9-17.
• Jickells, K. & Negrusz, A. (ed.) (2008), Clarke’s Analytical Forensic Toxicology, London: Pharmaceutical Press.
• Kennedy, M.C. (2009), “Postmortem Drug Concentrations”.
• Pounder, D.J. & Jones, G.R. (1990), “Post-mortem drug redistribution – a toxicological nightmare”, 45(3), pp. 253-63.
• Shepherd, R. (2003), Simpson’s Forensic Science, 12^th edition, London: Hodder Arnold