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Category Archives: crime lab

Criminal Mischief: Episode #27: ABO Blood Typing

Criminal Mischief: Episode #27: ABO Blood Typing

 

LISTEN: https://soundcloud.com/authorsontheair/27-abo-blood-typing

PAST SHOWS: http://www.dplylemd.com/criminal-mischief.html

SHOW NOTES: http://www.dplylemd.com/criminal-mischief-notes/27-abo-blood-typing.html

 

ABO Blood Type System

From FORENSICS FOR DUMMIES

By simply typing the blood at a crime scene, investigators narrow their suspect list and completely exonerate some suspects by using the population distribution information for the four ABO blood types. 

Population Distribution of ABO Blood Types

O: 43%

A: 42%

B: 12%

AB: 3%

Besides determining the ABO type, serologists are able to further individualize blood samples. RBCs contain more proteins, enzymes, and antigens than those used in the ABO classification system. These include antigens with such catchy names as Duffy, Kell, and Kidd and intracellular enzymes such as adenylate kinase, erythrocyte acid phosphatase, and the very useful phosphoglucomutase (PGM).

PGM is an enzyme that appears in many different forms, or isoenzymes, and at least ten of them are fairly common. Regardless of ABO type, a particular individual can have any combination of the isoenzymes of PGM. The ME and the serologist use that fact to further narrow the list of suspects for further DNA analyses and confirmation that they were capable of leaving a particular bloodstain.

For example, say that a stain is Type AB and has PGM 2. The ME knows the AB blood type is found in only 3 percent (see Table 14‐1) of the population, and PGM 2 is found in only 6 percent of people. Because these two factors are inherited independently, the probability of a particular individual being Type AB, PGM 2 is only 0.18 percent or less than 2 per 1,000. 

If the police find blood at the scene that matches the blood of a suspect who has Type AB, PGM 2 blood, the probability that that suspect is not the perpetrator is 2 in 1,000. Although not perfect, those odds still are much better than a coin toss. 

Testing for Paternity 

You inherit your blood type from your parents. For that reason, a serologist can assess paternity in many cases. The crime lab is often involved in paternity testing because paternity may be a critical component in determining child support, custody, and visitation. It also may play an important role in crimes and civil proceedings that involve kidnappings, insurance fraud, and inheritance conflicts. 

Inheriting your blood type 

ABO blood types, or phenotypes, come in only four varieties: A, B, AB, and O. But, for some blood types two genotypes, or gene pairings, are possible. A phenotype is what something looks like (in this case the ABO blood type), while the genotype is the underlying genetic pattern. We receive our ABO genes from our parents, one from Dad and one from Mom. 

The important thing to know in this system is that A and B genes are co-dominant (equally dominant), while the O gene is recessive. So someone who receives an A gene from one parent and an O gene from the other has Type A blood, but not Type O, because the A gene is dominant. 

Determining Possible Genotypes from Phenotypes 

Type A: AA or AO

Type B: BB or BO

Type AB: AB

Type O: OO

People with Type O blood must have an OO genotype. They can have neither an A nor a B gene because having one or the other dominates the O gene and produces either Type A or Type B blood. 

A person with Type A blood can either receive an A gene from each parent and thus have an AA genotype or an A gene from one parent and an O gene from the other for an AO genotype. Remember, A is dominant, so when it is paired with the recessive O gene, the A gene determines blood type. People with the AA and AO genotypes both have Type A blood, but genetically speaking, they’re different. 

Type A parents who have AA genotypes can provide only A genes to their offspring, because all their eggs or sperm have an A gene. But Type A parents who have AO genotypes can provide either an A gene or an O gene to their offspring, because half their eggs or sperm have an A gene, and the other half have an O gene. When both parents are Type A, several possibilities exist for the genotype their offspring will have.

In each of the scenarios presented in Figure 14‐1, the child’s blood type is Type A, except when both parents donate an O gene. In the latter case, the child’s genotype and blood type (phenotype) respectively are OO and Type O. These parents can’t have any offspring who have Type B phenotype or BB, BO, or AB genotypes, because neither parent has a B gene to donate. 

Determining Fatherhood

Blood typing can exclude paternity but cannot absolutely verify it. For example, a man with Type AB blood can’t father a child with Type O blood. So if a child has Type O blood, all men with the Type AB are ruled out as the child’s father. A man with Type A (genotypes AA or AO) blood can be the father, but only if he has an AO genotype. Men who have AA genotypes also are excluded. Men with the AO genotype, however, can’t be ruled out at this point. 

To dig deeper into this complex system grab a copy of either:

FORENSICS FOR DUMMIES: http://www.dplylemd.com/book-details/forensics-for-dummies.html

 

HOWDUNNIT: FORENSICS: http://www.dplylemd.com/book-details/howdunnit-forensics.html

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Criminal Mischief: Episode #07: Famous and Odd DNA Cases

 

Criminal Mischief: Episode #07: Famous and Odd DNA Cases

LISTEN: https://soundcloud.com/authorsontheair/criminal-mischief-episode-07-famous-odd-dna-cases

PAST SHOWS: http://www.dplylemd.com/criminal-mischief.html

 

FAMOUS AND ODD DNA CASES NOTES:

 

Colin Pitchfork: The Beginning

http://aboutforensics.co.uk/colin-pitchfork/

Timothy Wilson Spencer, The Southside Strangler” First US DNA Conviction

(David Vasquez—first to be exonerated by DNA)

https://en.wikipedia.org/wiki/Timothy_Wilson_Spencer

http://www.digitaljournal.com/article/352011

Brown’s Chicken Murders:

https://en.wikipedia.org/wiki/Brown%27s_Chicken_massacre

https://chicago.cbslocal.com/2018/01/08/browns-chicken-massacre-25-years-anniversary/

Lonnie Franklin, The Grim Sleeper: Familial DNA

https://en.wikipedia.org/wiki/Grim_Sleeper

https://www.rollingstone.com/culture/culture-features/grim-sleeper-serial-killer-everything-you-need-to-know-252246/

James Lynn Brown: Familial DNA

https://www.ocregister.com/2012/12/04/family-members-dna-solves-1978-killing/

Gary Ridgway, The Green River Killer

https://en.wikipedia.org/wiki/Gary_Ridgway

Pierre G: Kiss DNA Foils Jewel Thief

https://www.telegraph.co.uk/news/worldnews/europe/france/10616806/French-jewellery-thiefs-fate-sealed-with-a-kiss-after-conviction-from-DNA-on-victim.html

David Stoddard: Dog Bite DNA Case

https://www.news5cleveland.com/news/local-news/akron-canton-news/dna-from-dogs-mouth-solves-barberton-home-invasion-suspect-david-stoddard-also-charged-with-murder

Maggot DNA Case:

https://www.ncbi.nlm.nih.gov/pubmed/22971153

Willow Martin Arson Case and Potato DNA:

http://www.courant.com/breaking-news/hc-strippers-arson-drugs-0713-20160712-story.html

https://www.mycitizensnews.com/news/2018/05/woman-sentenced-to-8-years-for-arson/

 

 
 

Does Your DNA Contain Your Image?

DNA-Based Sketches

 

To say that DNA had revolutionized criminal investigations would be a huge understatement. Prior to DNA profiling, identifying a suspect with absolute certainty was more difficult. Fingerprints would work, of course, and eyewitness accounts, though flawed in many ways, could also help. But a criminal leaving behind biological evidence such as blood, semen, saliva, hair, skin cells, and other little bits, offers a method of identity that is second to none. DNA profiling has been used to catch many a criminal. But, in order for it to do its work, there must be something for the DNA analyst to compare the crime scene sample against. The DNA database, CODIS, helps because it stores millions of DNA profiles and if the perpetrator is in the system, a match can be made. But if he is not, the database is of little help.

DNA analysis can reveal the gender of the person who left behind the sample quite easily. But our DNA controls more than that. It determines how tall we will be, what our hair and eye color will be, our intellectual level, our ability to play music, and many other things. Familial DNA has been used to narrow down unknown samples to a smaller group, such as an extended family. And lately, this is been used in conjunction with the various ancestral databases to solve some crimes. But a newer technique offers another tool on the DNA front. It’s called DNA Phenotyping.

The principle seems simple: Since our DNA determines what we look like, would it not be possible to take a DNA sample and then create an image of the individual it belonged to? Maybe. At least great strides have been made in that regard. A case in point is that of research biologist Le Bich-Thuy, who was raped, battered, and strangled 24 years ago. DNA obtained from that scene was subjected to DNA Phenotyping and an image of the individual who likely perpetrated the crime was generated. Not only that, the image was age altered so that it would more accurately reflect what he might look like now. Fascinating case.

 

Improved GHB Testing

nmr

NMR Spectrograph

GHB is one of the so-called Date Rape Drugs—along with Ecstasy, Rohypnol, and Ketamine. I have an article on these on my website (See Below).

GHB has been difficult to detect, primarily because it’s rapidly metabolized (destroyed) by the body. But new techniques employing Nuclear Magnetic Resonance (NMR) Spectroscopy allow the detection of GHB metabolites (breakdown products) as much as 24 hours later. This gives investigators a longer time period to uncover GHB in a victim.

GHB can also often be found in the victim’s hair up to a month or more after exposure, but this testing is not as yet perfected.

https://www.forensicmag.com/news/2017/08/chemists-discover-marker-date-rape-drug-testing

http://www.dplylemd.com/articles/date-rape-drugs.html

https://www.ncbi.nlm.nih.gov/pubmed/25433016

More on the fascinating world of Forensic Toxicology can be found in FORENSICS FOR DUMMIES:

http://www.dplylemd.com/book-details/forensics-for-dummies.html

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Holmes, Thorndyke, Locard, Gross, and the Modern CSI

There are no bigger names in the history and development of modern crime scene investigation than French investigator Edmond Locard and his Austrian counterpart Hans Gross. These two men shaped the development of crime scene investigation and even today their techniques create the cornerstone of forensic science. Locard’s Exchange Principle underlies every forensic technique.

locard1

EDMOND LOCARD

hans-gross

HANS GROSS

They were also great fans of Sir Arthur Conan Doyle’s Sherlock Holmes and R. Austin Freeman’s Dr. John Evelyn Thorndyke. Locard even suggested that students of police procedure read the Sherlock Holmes stories and learn from his techniques.

Sherlock_holmes_paget_slider

Both the real-life investigators and the fictional ones had one thing in common: the careful and meticulous approach to any crime scene, taking care to collect all useful evidence, while not damaging or contaminating it.

In my book Forensics For Dummies, the methods and techniques used to evaluate a crime scene and collect evidence are explained in great detail. Check it out if you want to know more about the techniques that saw their origin more than 100 years ago.

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The Queen of Poisons and The Marsh Test

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Arsenic has, over the centuries, garnered many colorful names. It was called the “queen of poisons” because it was so readily available, easy to use, highly effective, and untraceable. Thus, it was used by many famous historical poisoners. Some called it the “king of poisons” but since over the years,  female killers have favored poisons, “queen” seems more apt. It was also called “inheritance powder,” for obvious reasons—-once the estate holder is dead and gone, the heirs can party down.

Arsenic is the nearly perfect poison. This was definitely true centuries ago when there was no way to trace it. But what about today, with modern toxicological techniques? Unfortunately, arsenic is still a pretty good choice for the poisoner. It’s not often looked for in unexplained deaths and its effects mimic many medical conditions, particularly neurological and gastrointestinal.

Back a couple of centuries ago, because of its common use, a method for finding arsenic in the dead or ill became an imperative. There were many steps along this path. This search for arsenic was essentially the beginning of forensic toxicology.

From HOWDUNNIT: FORENSICS

Arsenic had been a common poison for centuries, but there was no way to prove that arsenic was the culprit in a suspicious death. Scientists had to isolate and then identify arsenic trioxide—the most common toxic form of arsenic— in the human body before arsenic poisoning became a provable cause of death. The steps that led to a reliable test for arsenic are indicative of how many toxicological procedures developed.

1775: Swedish chemist Carl Wilhelm Scheele (1742–1786) showed that chlorine water would convert arsenic into arsenic acid. He then added metallic zinc and heated the mixture to release arsine gas. When this gas contacted a cold vessel, arsenic would collect on the vessel’s surface.

1787: Johann Metzger (1739–1805) showed that if arsenic were heated with char- coal, a shiny, black “arsenic mirror” would form on the charcoal’s surface.

1806: Valentine Rose discovered that arsenic could be uncovered in the human body. If the stomach contents of victims of arsenic poisoning are treated with potassium carbonate, calcium oxide, and nitric acid, arsenic trioxide results. This could then be tested and confirmed by Metzger’s test.

1813: French chemist Mathieu Joseph Bonaventure Orfila (1787–1853) devel- oped a method for isolating arsenic from dog tissues. He also published the first toxicological text, Traité des poisons (Treatise on Poison), which helped establish toxicology as a true science.

1821: Sevillas used similar techniques to find arsenic in the stomach and urine of individuals who had been poisoned. This is marked as the beginning of the field of forensic toxicology.

1836: Dr. Alfred Swaine Taylor (1806–1880) developed the first test for arsenic in human tissue. He taught chemistry at Grey’s Medical School in England and is credited with establishing the field of forensic toxicology as a medical specialty.

1836: James Marsh (1794–1846) developed an easier and more sensitive version of Metzger’s original test, in which the “arsenic mirror” was collected on a plate of glass or porcelain. The Marsh test became the standard, and its principles were the basis of the more modern method known as the Reinsch test, which we will look at later in this chapter.

As you can see, each step in developing a useful testing procedure for arsenic stands on what discoveries came before. That’s the way science works. Step by step, investigators use what others have discovered to discover even more.

I ran across an excellent article on the Marsh Test and it’s definitely worth a read. I can imagine when this was performed in the courtroom it did elicit a few gasps.

A few useful links:

http://www.dplylemd.com/book-details/howdunnit-forensics.html

http://www.atlasobscura.com/articles/marsh-test-arsenic-poisoning

http://www.huffingtonpost.com/sandra-hempel-/arsenic-the-nearperfect-m_b_4398140.html

http://www.dartmouth.edu/~toxmetal/arsenic/history.html

 

Howdunnit Forensics Cover

 

How Old Is That Fingerprint?

Fingerprint

Fingerprints are useful forensic science tools. They’ve been so for over 100 years. Mainly, it’s the pattern of the ridges on the fingertips that supply the useful information. We know that everyone has different fingerprints and we know that they do not change throughout the person’s life. This means that they are highly reliable sources for identification and for discrimination between two individuals. Law enforcement has employed this for years.

But several newer techniques and analyses allow investigators to go even deeper. The skin cells, that are part of a fingerprint, can often yield DNA. Chemicals in the print residue can sometimes reveal if the person has used or handled such substances as cocaine. Other analyses are underway that might make fingerprints even more useful.

One question that frequently plagues crime scene investigators is exactly when a print was laid down. This determination can make a huge difference. Let’s say that a print is discovered at a homicide scene and the primary suspect says that he had been at that location but that that had taken place a week earlier. Not on the day of the killing. Is he telling the truth? Or simply trying to throw the police off and make an excuse for the evidence they collected against him? It would be nice to know if the print was 24 hours old or seven days old.

Research is currently underway by Shin Muramoto and his colleagues and they reported their initial findings in a recent article in Analytical Chemistry. They discovered that a chemical found in fingerprints known as palmitic acid migrates away from the ridges at a predictable and consistent rate. By looking at this migration pattern they are able to determine whether the print is fresh or up to four days old. They are looking to extend this envelope to a longer period of time. But you can see, that even this level of discrimination could help—or not—- the suspect in the above scenario.

 
 
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