Author Forensic Question: DNA and Donated Blood

Today, I'm posting a forensic medical question I had for Amryn Cross.

Jordyn Asks:

Can you tell if blood from a crime scene is from a donated pint of blood? If so, how?

Amryn Says:

You can actually tell the difference. A donated pint of blood will only have red blood cells and not the other components of blood (white blood cells, platelets, etc.). When the DNA from the donated blood is tested, the scientist would probably think it odd that they got little to no DNA yield (red blood cells don't have nuclear DNA). They might chalk it up to degraded blood, or they might look at it under the microscope and find only RBC, which should make them suspicious. But probably the first indicator is that the blood at the crime scene would not clot if it were from a donated unit. The investigator may or may not pick up on that, but a crime scene tech probably would.

Jordyn Asks:

What about a pint of whole blood? Would it still be the same? Would small amounts of dry blood give DNA?

Amryn Says:

Whole blood would give DNA results but wouldn't clot, so that would be something they would have to pick up on at the crime scene. If it was suspected and they wanted it verified, tests could be done for the preservatives in the bag.

Yes, if they were just droplets, they would still dry over time. And as long as it's whole blood, it will give lots of DNA.

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Amryn Cross is a full-time forensic scientist and author of romantic suspense novels. Her first novel, Learning to Die, will be released in September. In her spare time, she enjoys college football, reading, watching movies, and researching her next novel. You can connect with Amryn via her website, Twitter andFacebook.

Author Forensic Question: Evidence of Pregnancy on Autopsy

Aray Asks:

Can an autopsy show evidence of a three week old fetus? I’m researching for a novel I’m writing and I need your help, considering that the information has to be accurate.

My MC’s mother’s body is severely mutilated ( carved into).  She was three weeks pregnant at the time this gruesome murder took place. Police officials accuse her husband of doing the deed.  Having no leads, they arrest him. The husband’s on trial for capital murder.  The medical examiner takes the witness stand. The lawyer asks him a series of questions, one being the autopsy report.

Amryn Says:

A 3 week old fetus would not be visible during an autopsy. At that point in development, the fetus is a ball of cells but without any physical characteristics that one would recognize as human. If the medical examiner needs to detect that the victim was pregnant, the best way would be to perform an HCG test on the victim's blood.

HCG is the hormone that is responsible for making a pregnancy test appear positive. It usually takes 3-4 weeks for this hormone to be at a high enough level to trigger a positive test, however a quantitative test might be enough to suggest that the victim's hormone levels were slightly above normal. I wouldn't think it would be enough for a medical examiner to definitively say the victim was pregnant, but it might be enough for he/she to say it's possible. Any time after 4 weeks, the HCG levels will begin to rise almost exponentially and therefore would be more easily detected.  

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Amryn Cross is a full-time forensic scientist and author of romantic suspense and mystery novels. Her first novel, Learning to Die, is available on Amazon. The first book in her latest series, loosely based on an updated Sherlock Holmes, is available for pre-order on Amazon. Look for Warzone in January 2015. You can connect with Amryn via her website, Twitter and Facebook.

Forensic Question: Solving Cold Cases

My question is about cold cases. Are you able to test for DNA from blood on a knife or clothes from 30-40 years old? Also, if the remains of a body were found in a mine shaft, could you tell the manner of death from that same time or even older, say, 150 years old? How would you do this and how long would it take? Thanks so much for your help!

Amryn Says:

Cold case investigations have come a long way with the use of DNA technology. Answers that would have been impossible 20 years ago are now commonplace. The problem with cold cases is often in the handling of the evidence. On the knife or clothes that you mentioned, when they were first collected from a crime scene 30-40 years ago, the investigator may not have worn gloves. That seems shocking given what we know now, but it wasn’t all that routine a few decades ago.

What that might mean for your DNA results is that you get a mixture—say, the victim’s blood and another unknown profile. Now, does that profile belong to the killer or just the detective or crime scene tech that handled the evidence without gloves? Without something to compare back to, you won’t be able to say.

Let’s assume best case scenario, though. If the bloody evidence was stored and handled properly, it is definitely possible to get a DNA profile from the blood present on a knife or on clothes. This can usually be done with routine DNA testing, which generally takes 2-3 weeks. Of course, for the purposes of fiction, the DNA could be “rushed” and then results would possibly be available as soon as 48 hours. This testing will probably be done at the police department’s or state’s crime lab.

As far as a body in a mine shaft, unless the body is frozen, it’s likely to be not much more than a skeleton by the time it’s found 30-40 years later, and certainly 150 years. However, if the manner of death was some sort of trauma (i.e. broken neck from a fall or stab wound where the knife grazes the bone), a lot can still be determined from bones.

In most cases, a forensic anthropologist would be the person to make that determination. Some states have one on staff while others call in an expert like Dr. Bass (founder of the Body Farm) when they are needed.  I would say the time frame for that sort of determination is at least a couple weeks, though I’m sure there are cases where it could be done faster. And I should also mention, many forensic anthropologists like to be present when the team is recovering the bones to make sure none are missed and to make observations based on the position of the bones.

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Amryn Cross is a full-time forensic scientist and author of romantic suspense and mystery novels. Her first novel, Learning to Die, is available on Amazon. The first book in her latest series, loosely based on an updated Sherlock Holmes, is available for pre-order on Amazon. Look for Warzone in January 2015. You can connect with Amryn via her website, Twitter and Facebook.

Forensic Question: Differentiating Twin Murder Suspects

Sarah asks:

If you have identical twins who are both suspects in a murder, how could you tell them apart?

Amryn says:

Identical twins are a hot topic in forensic DNA. Up until now, it’s been thought that identical twins have identical DNA and therefore are the perfect twist to a murder mystery. We’re finding out now that’s not necessarily true.

Strictly from a DNA perspective, research is showing that even twins have small minute differences in their DNA called SNPs (single nucleotide polymorphisms.) These aren’t routinely tested for in forensics because they’re pretty cutting edge, but such testing could be done (likely by a private lab) if the need arose.

Another option would be generating an antibody profile. When we’re born, we have an antibody profile like our mother. But beginning at birth and until the age of two, our antibody profile is evolving. It’s pretty much set in stone by the age of two and (as far as we know) doesn’t change throughout life. These antibodies are slightly different than the ones you make to fight off disease, but the important part is that they’re unique. Even identical twins will have different antibody profiles. This testing is new and is beginning to be used in conjunction with DNA testing.

Of course, this all depends on what type of evidence is found at a crime scene. Antibody profiling might be useful if some type of body fluid is found (i.e. blood, saliva, tears, sweat, etc.) but not so much with skin cells or hair. And, of course, even identical twins should have different fingerprints, so in a case such as this, DNA evidence might not be as strong as some other possible links.

If you’re interested in learning a bit more about antibody profiling, check out this article: http://www.americanlawyeracademy.com/antibody-profiling-forensic-evidence

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Amryn Cross is a full-time forensic scientist and author of romantic suspense novels. Her first novel, Learning to Die, will be released in September. In her spare time, she enjoys college football, reading, watching movies, and researching her next novel. You can connect with Amryn via her website, Twitter and Facebook.

Forensic Question: DNA Analysis

This question came to me via my blog as a comment but for some reason didn't post so I put Amryn to the task of answering it but am only using the poster's initials since she didn't give permission directly to use her full name.

It is related to Amryn's post on DNA analysis that you can find here.

S.C. Asks:

I understand that it becomes more difficult with half-siblings. But with full-siblings, if say, a brother suspected that someone was his sister, could he, through a blood sample, confirm the lineage if he did not have access to the parent's DNA?

Amryn Says:

This would definitely be possible. The best way to go about it would be to do mitochondrial DNA testing which traces the mother's lineage. So a brother and sister would have the same mitochondrial DNA because they share the same mother. To try to connect two people as siblings with the more common type of DNA testing is more difficult and would involve statistical calculations. The chance that full siblings will share one of their numbers (see the example in the post) at one of those locations on a chromosome is about 50%. So, yes, the brother could determine someone was his sister, but his best bet would be to have a mitochondrial DNA test done.

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Amryn Cross is a full-time forensic scientist and author of romantic suspense novels. Her first novel, Learning to Die, will be released in September. In her spare time, she enjoys college football, reading, watching movies, and researching her next novel. You can connect with Amryn via her website, Twitter and Facebook.