Presentation on theme: "Forensic Serology: Blood"— Presentation transcript:
1 Forensic Serology: Blood Written By: Alice YangPeriod 7Instructor Mary Villani
2 The Forensic Serologist The forensic serologist studies bodyfluids such as semen, saliva, and bloodmainly for identification purposes.Role(s):•Establishing type and characteristics ofblood•Blood testing•Examination of bloodstains•DNA typing•Preparation of court testimony &evidence
3 Blood Evidence Blood is the most well-known and significant evidence in the moderncriminal justice system.Blood evidence is important to the forensicinvestigator because:•It can link a victim to a suspect(Locard’s Exchange Principle]•Bloodstain patterns can reveal a greatdeal about position and movement duringthe crime•It has managed to destroy self-defensearguments of suspects
4 Forensic Value of Blood In forensic science, blood has always beenconsidered class evidence. However,individualized blood evidence is possiblein the near future. In fact, in some cases,forensic serologists were able to link asingle perpetrator to a bloodstain withstrong probability estimates.
5 Nature of Blood: General Characteristics Blood is a slightly alkaline fluid thatcirculates throughout our bodies,nourishing our cells, and transportingoxygen and waste. The fluid portion ofblood consists of plasma and serum, whilethe non-fluid portion consists of red bloodcells.Blood is composed of:•Water•Cells•Enzymes•Proteins•Other inorganic substances
6 Nature of Blood: Serum Serum is characterized by its yellow hue, and contains white blood cells andplatelets. Forensic analysts are able todetermine the freshness of a blood sampleby examining serum because it clotsseveral minutes after exposure to air. Acentrifuge can be used to separate theclotted material from the serum portion. Inaddition, serum contains antibodies ,proteins floating in blood fluid, which havesignificant forensic implications.
7 Nature of Blood: Red Blood Cells Red blood cells, the most prevalent bloodcells in the human body, are the primarymeans of delivering oxygen from the lungsto the body’s tissues via the blood. For redblood cells, the forensic analystsearches for smaller chemical substancesresiding on their surfaces, such asantigens , which also tend to haveimportant forensic implications.
8 Blood Grouping The A-B-O system of blood typing was discovered in 1901 by Dr. Karl Landsteiner.During the late 1930s, a series ofantigen-antibody reactions werediscovered in blood, the most commonones being ABH, MN, Rh, and Gm. There aremore than 256 antigens, and twenty-threeblood group systems based on associationwith these antigens. A fundamentalprinciple of serology is that for everyantigen, there exists a specific antibody. Infact, all blood groups are defined by theantigens on their red blood cells and theantibodies in their serum.
9 Blood Typing Blood typing requires two antiserums: anti-A and anti-B. By inserting a droplet ofthese antiserums in samples of blood, onecan determine which samples maintain anormal appearance and which samplesbecome clotted, or agglutinated, undermicroscopic examination. Type-A blood willbe agglutinated by anti-A serum; Type-Bblood will be agglutinated by anti-B serum;Type-AB blood by both; and Type-O blood byneither.
10 Rh Factor Blood can also be categorized using the Rh (Rhesus disease) factor. If an individualhas a positive Rh factor, this means thathis/her blood contains a protein that isalso found in Rhesus monkeys. Approximately 85% of the population has apositive Rh factor, and doctors are trainedto monitor closely any woman who is Rhnegative and becomes pregnant. The Rhfactor, like other antigens, can be found onthe surface of red blood cells.
11 Individualization of Blood The potential for the individualization ofblood is based on the typing of proteins andenzymes. Blood proteins and enzymes havethe quality of being polymorphisms oriso-enzymes , which means they exist inseveral forms and variants. Most peopleare familiar with at least one commonpolymorphism in blood: Hb, which causessickle-cell anemia.
12 Secretors In 1925, a blood-related discovery valuable to forensic science was made.Approximately eighty-percent of the humanpopulation was found to be "secretors,"individuals whose specific types ofantigens, proteins, antibodies, andenzymes characteristic of their blood canbe found in other bodily fluids andtissues. In the case of a secretor,investigators can conclude the blood typeby examining the saliva, teardrops, skintissue, urine, or semen. In a rape case, forexample, where the perpetrator is asecretor, potential suspects can benarrowed down through blood typeanalysis.
13 Bloodstain Analysis: The General Questions During bloodstain analysis, the forensicinvestigator uses these five specificquestions as guidelines for determiningthe nature of a crime.1. Is the sample blood?2. Is the sample animal blood?3. If the sample is animal blood, from whatspecies did it come from?4. If the sample is human blood, what typeis it?5. Can the sex, age, and race of the sourceof blood be determined?
14 Bloodstain Analysis: Blood or not? To determine whether or not blood ispresent at a crime scene, forensicinvestigators use color or crystalline tests.In the past, police investigators weretrusted to verify the presence or absence ofblood, but Miller v. Pate (1967) enforced thatphysical tests should be completed in thesearch for blood. The Benzidine test waswidely implemented until it was discoveredto be a known carcinogen. The currentKastle-Meyer test, which uses thechemical, phenolphthalein, operates on thefact that when phenolphthalein comes incontact with hemoglobin, it releasesperoxidase enzymes that cause a brightpink color to appear.
15 Bloodstain Analysis: Blood or not? In order to detect invisible bloodstains,forensic investigators use the luminol test.Luminol, a chemical sprayed on carpetsand furniture, reveals a slightlyphosphorescent light in the dark wherebloodstains (and other stains) are present.Long-dried blood has a tendency tocrystallize, or can be made to crystallizewith various saline-acid mixtures. Thenames of various crystal tests are theTeichman test , the Takayama test , andWagenhaar test.
16 Bloodstain Analysis: Animal Blood? To determine whether blood at the crimescene originated from an animal, forensicinvestigators use antiserum or gel tests.Establishing whether or not blood is animalblood is significant because any possibilityof an injury to the household pet, caused bya perpetrator or another animal, must beeliminated. Pets generally spread humanbloodstains throughout the crime scene,but the pet can be a victim, perpetrator, orwitness (through the cross transfer ofevidence between the animal’s DNA and theperpetrator). Veterinary forensics may be anecessary unit if pets are involved in thecrime.
17 Bloodstain Analysis: Animal Blood? To determine whether blood is animal orhuman in origin, the precipitin test isconducted. This process involves injectingan animal, usually a rabbit, with humanblood. The rabbit's body createsanti-human antibodies, which are thenextracted from the rabbit's serum. If thisantiserum is then placed on a sample fromthe crime scene, and the blood displaysclotting, the forensic investigator canconclude that the blood is human blood.The same procedure of creating andextracting antiserum can be applied toevery known animal.
18 Bloodstain Analysis: Human Blood? To confirm whether blood is human inorigin, the forensic investigator must firstdetermine that he has an adequate andquality blood sample. A blood sample thatmeets these requirements can undergodirect typing using the A-B-O system. Ifseverely dried stains are uncovered,indirect typing should be completed usingtechniques such as the absorption-elutiontest. During this test, the forensic scientistadds compatible antiserum antibodies to asample, heats the sample to break theantibody-antigen bonds, and finally insertsknown red blood cells from standard bloodgroups to see what coagulates.
19 Bloodstain Analysis: Age, Sex, & Race To estimate the age, sex, and race usingblood found at the crime scene, theforensic scientist uses various color andnitrate tests, and applies heredityprinciples to his tests. Unfortunately, noexact determinations are possible.However, clotting and crystallization canhelp approximate age, testosterone andchromosome testing can help determinesex, and certain racial genetic markersinvolving protein and enzyme tests canhelp establish race.
20 Blood & Crime Scene: Wet vs. Dry Blood Wet blood is more significant than driedblood because the forensic scientist canperform more tests in order to gain insightto the happenings of the crime. Forexample, alcohol and drug content can bedetermined from wet blood only. Bloodbegins to dry after three to five minutes ofexposure to air. As it dries, it changes colorfrom a deep red towards brown and black.Blood can be categorized into pools, drops,smears, or crusts.
21 Projection of Blood Forensic investigators can determine how blood was projected from the body byexamining factors such as:Type of injuriesThe order in which the wounds were receivedWhose blood is presentThe type of weapon that caused the injuriesWhether the victim was in motion or lying still when the injury was inflictedWhether the victim was moved after the injury was inflictedHow far the blood drops fell before hitting the surface where they were found.
22 Blood & Crime Scene: Categories of Blood Patterns Pools of blood have evidentiary value incollecting a wet sample. Drops of blood canreveal the height and angle from which theblood fell onto the surface. According toforensic scientists, the blood spatteranalysis claims that blood which fallsperpendicular to the floor from a distanceof zero to two feet would create a circulardrop with slightly frayed edges. Drops froma higher distance would have more distincttendrils extending off the edges.
23 Blood & Crime Scene: Categories of Blood Patterns A blood smear on the wall or floor canindicate the direction of force of theblow. The direction of force is always in thedirection towards the tail, or smaller end, ofthe smear. In other words, the largest areaof the smear is the point of origin. Bloodcrusts must be tested with crystallinetechniques to verify that they are actuallyblood. Refrigerated red blood cells have ashelf life of about forty-two days, and theserum containing white blood cells can berefrigerated much longer, almost up to ayear. DNA can be extracted from blood (ifwhite blood cells which always contain anucleus are present), and also from sperm,bone marrow, tooth pulp, and hair roots.
24 Blood & DNA Testing Blood is used in DNA testing, as shown by the following steps:1. Blood samples are collected from thevictim, defendant, and crime scene.2. White blood cells are separated from redblood cells.3. DNA is extracted from the nuclei of white4. A restrictive enzyme is used to cutfragments of the DNA strand.5. DNA fragments are put into a bed of gelwith electrodes at either end.6. Electric current sorts DNA fragments bylength.7. An absorbent blotter soaks up the imprint; itis radioactively treated, and an X-rayphotograph, called an autoradiograph, isproduced.
25 Blood & Crime Scene Regardless of what type of analysis is used on the blood at the crime scene, care mustbe taken to handle it properly and toprevent putrefaction. Photographs andnotes should be taken before any blood islifted. Samples should not be exposed toheat, moisture, or bacterial contamination,because these factors can shorten thesurvival time of proteins, enzymes, andantigens. Delays in bringing samples to thelab must be avoided at all cost, because itcan diminish evidential value.
26 Court Significance Experts in bloodstain examination are usually law enforcement personnel. Incertain jurisdictions, a police investigatoror blood specialist may testify on the coreissue because blood evidence is usually avital aspect of the crime scene.An expert in bloodstain examination has:•Completed specialized training•Conducted a sufficient number ofexaminations•Accumulated enough reference patternsto reinforce an argument