If reference samples of blood from both parties are provided, then it can be determined if they have the same ABO blood type. If they do, then further analysis of the reference blood samples may show that the two parties have different PGM types.
The unknown stain could then be analyzed for the genetic marker PGM. This analysis may then show the possible origin of the stain.
Suitable reference samples a suitable reference sample is collected directly from a person into a tube or "Vacutainer" from all of the involved subjects must be sent to the crime lab. An unsuitable reference sample is bloody clothing or some other bloody item. These are unsuitable because the histories of these bloodstained items are usually questionable and there may be factors present on the items that will give misleading results.
The sample must be collected in the proper "Vacutainer. This is a summary of the forensic uses of "Vacutainers":. Useful for conventional serological tests; less useful for DNA testing; can be used for pregnancy and HIV testing 4 if a yellow top is not available, then the author prefers receiving red top and purple top Vacutainers from a subject.
Useful for toxicological testing; not suitable for conventional serological analysis 5 and may not be suitable for DNA analysis. If the investigator is collecting blood from an autopsy, then one of each type of Vacutainer should be collected from the victim. This will insure that any necessary forensic testing can be performed. These Vacutainers should be stored in a refrigerator not frozen at about four degrees Centigrade until they are transported to the crime lab.
In recent years, blood visualization enhancing chemicals have regained popularity with crime scene investigators. The chemical of choice is usually luminol. Luminol is a chemical that when applied to bloodstains, even very dilute bloodstains, will cause the bloodstains to glow in the dark. Because it has several drawbacks as a presumptive test for blood, spraying luminol at a crime scene should be an investigator's last resort for detecting blood.
The problems with luminol include:. Unfortunately, some crime scene investigators use luminol as their first choice for detecting blood. By using luminol in such a reckless manner, it is possible to lose valuable information from a bloodstain. When searching for blood at a crime scene, especially blood that may have been cleaned up, the investigator should first use a high intensity light to search for any traces of blood.
Bloodstains are not easy to eradicate. Diluted blood will often leave a brownish stain where a person has tried to clean it. Blood also has a tendency to flow into floorboard cracks, into carpet padding, behind baseboards, etc. By conducting a thorough examination with a high intensity light source, the investigator can usually find these areas.
These items can then be removed or collected and submitted to the crime lab for confirmatory testing. Because luminol is so sensitive to dilute bloodstains, it is occasionally used to enhance bloody impressions shoeprints, fingerprints, etc. Luminol is not the best reagent for enhancing these impressions because of its water base. Better methods for enhancing bloody impressions use either rapidly evaporating organic solvents such as merbromin and ortho-tolidine or they use a water based chemical after treating the impression with a fixative such as the amido black staining technique.
Once the investigator realizes the potential of blood evidence as well as problem areas in documenting, collecting, and preserving this type of evidence, he or she will be more effective in finding the best bloodstains. Some commonly encountered problems are lack of communication especially between the investigators and the forensic scientists , unfamiliarity with the types of bloodstain analysis, lack of knowledge about which stains will yield the most useful information, poor reference samples, and indiscriminately using luminol at crime scenes.
If these problems are solved, then the blood collection and analysis should progress without any major problems. An investigator should take a slow and methodical approach to collecting and preserving evidence. The only time that an investigator should make rapid decisions concerning evidence is when the evidence is in danger of being destroyed or compromised. In that case, the evidence should be preserved, or documented and collected as quickly as possible.
Before setting foot in the crime scene, the investigator must gather as much information as possible to determine the scope and value of any evidence that may be present. This information may include witness statements, suspect statements, victim statements, information from the first responding officer, information from the detectives, etc. The investigator should then use logic and common sense to search for evidence; however, he or she should also use imagination and avoid becoming narrow-minded.
As investigators become more experienced, they know that certain patterns emerge and certain elements are common among similar cases. They also know that they have to keep an open mind when deciding what is evidence and where it will be found.
This is due to the unpredictable nature of people and the forces of chaos. Once the investigator has gathered as much information as possible about the case, then he or she should form a mental or written plan to proceed with the documentation, collection, and preservation of the evidence.
The investigator should also pass any relevant information to the lab analyst. This will allow the analysis to make decisions concerning the best approach to the analysis and what information can be determined from the evidence. The investigator should thoroughly document every aspect of the crime scene investigation from the initial walk through to the securing of the collected evidence.
Documentation is necessary to record the condition of the crime scene and its related evidence as closely as possible to their original condition at the time of the crime. Of course, there is usually some alteration of the scene that will occur between the time of the crime and the time that the scene is documented.
EMS personnel, police officers, and fire fighters may have to alter the original scene in the course of performing life saving measures. Other people entering the scene may also unknowingly or unconsciously alter the scene. The investigator has a number of tools available for documenting evidence including notes, videotape, photographs, sketches, and chain of custody forms.
The investigator may elect to use several or all of these methods of documentation. This documentation will also be used in the future to refresh the investigator's memories of the case. The first tool for documenting the crime scene investigation is note taking. An investigator should be as thorough as possible when taking notes. All of the pertinent times and actions taken should be recorded, such as who contacted the investigator and when; when did the investigator leave for the crime scene; when did the investigator arrive at the scene; what actions were taken by the investigator and when; when did the investigator leave the scene, etc.
Notes should be recorded throughout the entire crime scene investigation. Examination of the crime scene will usually begin with a walk through of the area along the "trail" of the crime.
The trail is that area where all apparent actions associated with the crime took place. This trail is usually marked by the presence of evidence. Point of entry, location of a body, areas where the suspect may have cleaned up, and the point of exit are all included in the trail.
The purpose of the walk through is to note the location of potential evidence and to mentally outline how the scene will be processed. The walk through begins as close to the point of entry as possible.
The first place the investigators should examine is the ground on which they are about to tread. If any evidence is found, then a marker should be placed at the location as a warning not to step on the item of interest. When searching for blood evidence, it is important to use a high intensity light. A high intensity light source will aid in the visualization of bloodstains, even stains that have been diluted. The light source can also be used to provide oblique side lighting.
Oblique lighting is an excellent tool for finding trace evidence and other small items of interest. As the walk through progresses, the investigators should make sure their hands are occupied by either carrying notebooks, flashlights, pens, etc. This prevents the investigator from depositing unwanted fingerprints at the crime scene. As a final note on the walk through, the investigators should examine the areas above their heads ceiling, tree branches, etc.
These areas may yield blood spatters, bullet holes, etc. Videotape can be an excellent medium for documenting bloodstains at a crime scene. If a video camera is available, it is best used after the initial walk through.
This is to record the evidence before any major alterations have occurred at the scene. Did the stain patterns come from the victim or someone else? Are there other scene factors e.
To help reconstruct events that caused bloodshed, analysts use the direction and angle of the spatter to establish the areas of convergence the starting point of the bloodshed and origin the estimation of where the victim and suspect were in relation to each other when bloodshed occurred.
To find the area of convergence, investigators typically use string to create straight lines through the long axis of individual drops, following the angle of impact along a flat plane, for instance the floor or wall where the drops are found. Following the lines to where they intersect shows investigators where the victim was located when the drops were created. To find the area of origin, investigators use a similar method but also include the height calculations.
For example, if the area of origin is determined to be only two feet above the area of convergence on the floor, the analyst may presume the victim was either lying or sitting on the floor. If it is five feet above the convergence, the victim may have been standing. This analysis can be done using strings and a protractor, mathematical calculations or computer models. BPA can range from investigation and analysis of bloodstain patterns at the crime scene to bench work in the laboratory analyzing and DNA profiling the blood.
Limited analysis can also be done using only photographs of the scene. Left: large volume blood stain. Right: impact spatter pattern. Left: passive bloodstains. The reason for this distinction is that physical evidence can be measured numerically while testimonial evidence is more subjective in nature. Each individual remembers events in a slightly different way and even observations of things like color depend on the individual's visual ability to discern different hues.
Another way to look at the two types of evidence or data is that physical evidence is objective and testimonial evidence is subjective.
Crime Scene Evidence Eric Liou. As you saw on the previous slide there are many different types of evidence and as a result there are many ways in which to collect and preserve these types of evidence. The stress on the word preserve is deliberate. Just collecting evidence does not mean that it will remain intact and unchanged between the time it is collected and analyzed.
Steps must be taken to be sure the evidence does not degrade. The collection and proper preservation of evidence will now be discussed. Pay close attention since in just a few weeks you will need to put these techniques into practice. Blood and crime scenes seem almost synonymous, you can't have one without the other. This is not completely true but Blood is one type of evidence that can provide large amounts of data for an investigation blood type, DNA, etc.
Blood that is in a liquid form should be picked up on a gauze pad or other clean sterile cotton cloth and allowed to air dry thoroughly, at room temperature. Once dry, It should be refrigerated or frozen as soon as possible and brought to the Laboratory as quickly as possible. Because DNA and other components in the blood decay rapidly, a delay of more than 48 hours may make the samples useless.
You obviously cannot dry a blood stained sheet or shirt at the crime scene itself so you must prepare these samples for transport.
At the crime scene, you should label and roll the evidence in paper or place it in a brown paper bag or box and seal and label container. Never place more than one piece of evidence in a container. Any never use plastic containers.
The lack of ventilation in plastic promotes decay and will destroy the blood evidence before you can get it to the lab. You might think that drying the stain faster would be a good way to preserve the stain but you cannot heat the stained material or place it in bright sunlight to dry as this will degrade the biological value of the stain.
If this method is used it is important for investigators to not touch the sticky side of the tape with bare hands and the investigator should run an eraser or some type of blunt object over the placed tape to ensure that contact is made with the dried stain. The lifted stain is then be packaged and labeled, then delivered to the laboratory. Another way to collect a sample off of an object is to use a clean sharp object to scrape flakes of the stain into a paper packet.
The last two methods of collection of a dried bloodstain on a large object require the use of distilled water to dampen the stain before rolling a thread in the stain or absorbing the stain with a cotton square.
These two methods are not recommended due to the risk of contamination. When dried blood is found on clothing the entire article of clothing should be packaged and labeled and delivered to the lab.
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