Rape Kit Testing

Stan Asks:

My question for you is would a rape kit routinely be used to test for evidence of chemicals found in a condom in addition to DNA or would further tests be required? My plot has a woman getting even with a man by having her girlfriend havesex with the guy (he’s using a condom). She then gives the material to her friend who applies the sperm and claimsshe was raped.



Amryn Says:

Rape kits are routinely tested for the presence of semen and sperm and maybe saliva depending on the story the victim gives. Chemicals found in spermicide and other condom components aren’t something an analyst would test for. Depending on how long of a time lapse between intercourse and the woman applying the sperm, it’s possible the spermicide on the condom would have already degraded the sperm to the point that it isn’t detectable, but that would only occur after a long time.

 More likely, when DNA testing was performed, it would yield a mixture of 3 profiles: the man, the woman’s friend, and the woman. This is because the woman’s friend’s profile would likely be present on the condom from the intercourse she had from the man. This might raise a red flag but it would be up to the investigator to look into it further.

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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 websiteTwitter andFacebook.

Author Forensic Question: Planting DNA Evidence


Question:


I’m considering writing a crime novel that involves the antagonist framing others for crimes he has committed. He is a genius level sociopath who studies his victims’ habits by analyzing their trash.  His day job is with the local trash company (handy for him.)

Now the question. Can he use semen from a condom (if it’s not too old) to plant on/in a victim? He rapes, kills, and then plants the evidence along with other clues that lead to his intended second victim?

Amryn says:

This is a great scenario for a novel and would certainly throw the police off for a while. For the antagonist to pull this off, he will need to take some precautions. First of all, if he rapes the victims himself, he’ll most certainly need to wear a condom. Secondly, how he kills his victims will be important in determining if he’s left any of his DNA behind. For instance, if he strangles them with his bare hands, it is possible his DNA could be found from a swab of the victim’s neck. The use of a knife would run the risk of cutting himself and leaving his own DNA behind that way.

As far as planting the evidence, that’s certainly possible. In fact, the reverse of this has been done in real life. A man was put in prison for rape, largely because of the DNA evidence against him. While he was in prison, he placed some of his semen in a ketchup packet and smuggled it out to a female friend. She then planted the semen on herself and said she’d been raped. When they collected the evidence and processed it, the DNA came back to the man who was in prison—a pretty good alibi for the time of the rape. He insisted that the DNA results must have been wrong in the first place or someone else had his DNA profile. Of course, his scheme didn’t work, and as far as I know, he’s still in prison. All that to say, yes, planting that sort of evidence is definitely possible.

If your antagonist takes the condom from someone else’s trash, he runs the risk of having another person’s DNA present as well. When things are thrown away, DNA from several sources (presumably everyone who lives in the house) will come in contact with other objects and transfer will happen. There might not be significant enough transfer to matter, but it could result in the bad guy inadvertently transferring the male’s DNA as well as his partner’s DNA to the victim. If that’s his intention, there’s no problem, but it could also provide a way for your hero to figure out that something just doesn’t seem right about this.

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Amryn Cross is a full-time forensic scientist and author of romantic suspense and mystery novels. Her 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 onAmazon. Look for Warzonein January 2015. You can connect with Amryn via her websiteTwitter 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 onAmazon. Look for Warzonein January 2015. You can connect with Amryn via her websiteTwitter and Facebook.

Forensic Question: DNA Testing Turn Around Time

Amanda asks:

How long does it typically take for DNA results to come back in a murder case, specifically blood on a knife? Could the agency get a preliminary report (i.e. blood type) any faster?

Amryn says:

Each lab will have its own turnaround time for DNA. For most state crime labs or local agency labs (meaning those that are attached to a law enforcement agency) the turnaround time is likely to be several weeks/months. This is because they may receive dozens of cases per day, certainly per week, and cases are usually worked in the order they are received. Some cases may only have one or two samples that need DNA testing, while others may require 40 or 50 (this is not as common, but not unheard of either.)

In some cases, a district attorney or someone in charge of the lab may declare the case a “rush” or an “expedite” (usually documented in the form of a letter), in which case it jumps to the front of the line. A lab may drop everything else to work on this case, depending on the scope of the case. Usually one analyst is assigned a case, but may ask others for help to get the results out faster.

Best scenario (which never happens), DNA could possibly be done on an exhibit as small as a knife in 48 hours. Then the report has to be reviewed by two other analysts before it can be sent to law enforcement. That’s not including a search of the FBI database if there are no suspects in the case. A manual search of the database may be done in rare cases, otherwise it’ll take another week to see if the DNA profile “hits” anyone in the database.

Most places don’t do blood typing anymore because it’s kind of time consuming and obviously not as unique as a DNA profile. The most that could be said in a preliminary report is to verify that the stain on the knife is, in fact, blood. It seems silly, but they do have to verify that it is blood and not cocktail sauce or something on the weapon.

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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: 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.

Author Question: Lab Specialization

This post is related to Amory Cannon’s guest blog about DNA testing that posted a few months back.

Patti asks: Why wouldn’t a lab do DNA testing?

Jordyn says:

Labs specialize just like doctors do– in a sense. All labs can’t do all things. Even a hospital based medical lab doesn’t test for ALL medical diseases. Some, very specialized tests, can and do go to big research centers (like the Mayo clinic.)

It just isn’t financially reasonable for each lab to do all types of testing. For instance, a hospital based lab isn’t going to do forensics testing. In fact, I’ve not been part of a hospital that did paternity testing. If even collected, these would be referred to a lab that specialized in DNA testing.