Forensics for Writers: The Gold Standard

Next week will be the wrap-up, but as I said last week, DNA needed a post all it’s own. I’m going to get more into the speculative here, this is a fascinating and rapidly changing field when it comes to any aspect of science, not just forensics.

DNA (deoxyribonucleic acid, and isn’t that a lovely thing to say ten times fast) is considered the gold standard because of two things. One is based on math – the probabilities of two people matching across 13 alleles is something approaching billions if not trillions to one. With this in mind, if we have that full loci match, we can assuredly say that this person shed/bled/left this bit of DNA at the crime scene. Which isn’t to say that they did it, but I’ll get into that in a bit. The other reason this is the gold standard is television. The TV shows may get 90% of their stuff wrong, but this doesn’t matter to the general public. And the jury is drawn from the general public. The result is that juries almost demand there be DNA evidence presented to them.

With modern technology, DNA can be extracted, amplified, and sequenced from a single skin cell. Even hair, which unless it has been yanked out and retains the follicular tag, has no nuclear DNA, contains mtDNA and can be used to narrow down the identification of a suspect or a victim. The problem, of course, is finding that single cell to work with. DNA, like any other evidence, has drawbacks. For one thing, although the cost is falling and the time to run tests is going down with it, it’s still not a cheap or easy test to run. A skilled technician is needed to run the process, and interpretation of the results isn’t always clear-cut.

Imagine this. There’s a crime scene, and it’s been swabbed for DNA and tests are being done. We’re talking swabbed down to the single-cell collection point, and it’s a house where, say, drugs were being sold. Random people in and out all the time. The investigator had tried out a new shampoo and it made his scalp react and he’s got dandruff. The first officer on scene sneezed. The victims were stabbed and staggered through the house leaving bloodtrails everywhere until they died on the kitchen floor. A young woman and her dog (don’t kill the dog in a story. Readers hate that). So we have contamination, commingled blood from two humans (at least, the killer(s) cut himself) and a dog, and oh, yeah, it’s August, they didn’t have air conditioning and it must be 40 deg C in the house by the time they were found. At that temperature, DNA starts to break down. Or, wait, even worse – they got out to the end of the backyard and died in the little creek back there. Water. Water is not the forensic scientist’s friend.

gel electrophoresis
Pipetting samples for gel electrophoresis, the old-school way of looking at DNA.

While I know I could separate out the dog’s DNA from the humans, interpreting commingled DNA is a challenge, and that first uniform who sneezed (vomiting would almost be better because then the later investigators would have known about it. The sneeze was barely noticed by the guy, and he certainly didn’t think to tell anyone) meant that there will be an unknown profile in the samples near the side door where the attack initiated. There will also be profiles from people who were in the house recently. It’s going to be complicated, messy, and expensive. In a murder investigation, this isn’t really a factor, but in a lesser crime like a robbery, no department is going to this level to investigate.

DNA is not cut-and-dried, and as you write your story, this can be either a good thing or a bad thing. Good because we aren’t yet at a level of technology that allows every crime to be solved simply by scanning DNA at the scene and proclaiming ‘Eureka! ‘Twas him!” within minutes. Even when on-site DNA testing is possible – and it’s coming – there will still be all the complications I touched on in my scenario, plus more I couldn’t work in there. I’m not downgrading the on-scene investigators, I’ve sat in classes with some of them, been taught by another, but the reality is that they aren’t trained for everything that I’ll be trained for, and I won’t be trained in some aspects of their job (although the other half of my degree is Investigation). The lab and the field aren’t the same. Even if you’re writing science fiction in the future, complete detection, interpretation, and analysis of DNA is going to remain more complex than waving a magic wand. Although there’s an interesting story idea there using Clarke’s Law…

And the bad thing about DNA can actually be helpful to the writer. Introducing conflict, and tension, by having DNA not come back usable can be useful. Your investigator will have to work harder. Your villain will have to try to be sneaky in weird ways as they attempt to leave no DNA behind them… which will mean they miss something by over-focusing on that. Writers dream up hyper-intelligent criminals, but in the real world most of them are doofuses, to steal a word from Peter Grant (I always enjoy the Doofus of the Day posts when I catch them on his blog). We don’t need DNA to convict the doofuses of the world, but as I said above, juries expect it. When the proceedings go to trial, which doesn’t happen much of the time.

DNA may not be the miracle drug of the forensic world, but it does come close. I’ve enumerated some of the flaws, but it remains the most individual and solid of evidence in a case. In a few short decades, we have come from needing a lot of DNA material (blood or semen, usually) to being able to accurately process a profile from touch DNA – the shed skin cells left on a doorknob, for instance. I know I said that I don’t think there will ever be a magic wand, but I do think that with a trained, skilled operator, that wand might start to approach magical. I also think that public perceptions of DNA and what it can be used for, which might not be accurate, may drive policy and legislation in unexpected directions.

DNA databases are the other half of this tool. Once you have a profile, what do you do with it? From the TV, and books about crime, I suspect most of you are already familiar with CODIS. What some of you may know, and something that has implications for us as people as well as writers, is that the Supreme Court has ruled that anyone arrested for a major crime can have a DNA sample taken and entered into the database. Arrested – not convicted. Above and beyond the implications of this, are the growing privately held databases of DNA that are being created for genealogy purposes. What if your investigator is given access to one of those? I’m sure there are contracts between the company and the individuals who send in their samples to be told how much of a Neanderthal they are… surely there is some kind of privacy shield in place. People are too savvy to just let their DNA be stored anywhere on any old server (reached in and shuts off internal snark button) Ahem. Where was I? Oh, yes… could your investigator, armed with a warrant and Truth and Justice on his side, gain access to these private databases?

What about the movement to have everyone sampled at birth? What if this goes on?

And with that, I shall leave this topic. Next week, I’ll wrap up and answer any lingering questions.

And now, for something completely different: Shameless Self Promotion

I’ve had a new book published this week. It’s not a novel. In fact, it’s something that you don’t get in a fiction book – it’s an audience participation book. And it’s not available as an ebook.

I’ve produced a coloring book. It’s a bit like a chicken laying a Roc egg, you’re left wondering how this happened, and where did that come from?

I’ll blog in a couple of weeks here on the MGC about the nitty-gritty of producing a book that is primarily illustrations, because it was very different and a pain in the patootie.

But here it is. Dragons and flowers and cats and all the cute. My art isn’t fierce, it’s fun and cute. Inktail & Friends isn’t your typical adult coloring book – it’s suitable for kids (with motor control, some of the art is very detailed) all the way up to the grown-up who wants to play outside the lines as well as coloring in. It’s all my work, most of the books out there are simply public domain clip art, but I wanted to be different.


36 thoughts on “Forensics for Writers: The Gold Standard

  1. Back in the late 80’s I did my required English paper on DNA fingerprinting. Man it was hard finding information on criminal aspects of it. I ended up filling up the last couple of pages with stuff on it’s use in paternity cases (which is what it was used for mostly at that point) and some cases where it was used for determining the relationship between various endangered species (like tortoises). Things have changed so much in the last 3 decades.

    1. The later 80s would have been the infancy of the forensic use of it – I think the first use in a criminal case was ’87 – but it was used for civil cases first. And yes, it’s been a fast change. From poor prosecutors (snerk) standing there trying to explain what it was to incredulous jurors, to the jury wanting to know why they aren’t seeing it in evidence.

      1. PCR (Polymerase Chain Reaction – I may have spelled that wrong) was just being talked about as THE cutting edge technology for DNA. I think my criminal examples were one rape case in Florida and one murder in the UK. And then some paternity cases in UK and NJ (I can’t remember exactly now). Searching was a little slower then. Everything was hunt through the old card catalog in the public library and the local University, which didn’t even have computers that either the public or the check out desk could use. And then having to wait for the Inter-Library Loan to get processed so I could get the journals/mags.

        1. And here I am doing PCR in labs this semester like it’s no big thing 😀 I know, I’m always amazed when I look at just how quickly this happened. (you spelled that right, by the way).

        2. I recall reading an article (it might even have been the cover feature) in Science News about this fantastic new molecular amplification technique that could detect minute amounts and cascade to show “Found it!” in a big way. Yep, Polymerase Chain Reaction.

  2. Neat article. And perfect timing on the coloring book. Red 2.0 has a birthday looming. (And I’ve already been informed that 2.0 is far too young for Hello Kalashnikitty, or My First Waterballoon Cannon, or TMIAHM kinetic experiment set.)

    1. too young for waterballoon cannon? Noooo…

      LOL! I do hope the coloring book assauges some of the yearning desire for world destruction – there’s a bit of conflict between the cats and dragons. Can’t think *where* that concept got into my head. 😉

      1. 2.0 is at the more enthusiasm than aiming skills phase, so Aunt Red has been informed that projectile launchers are off the list. *sigh*

        Conflict between cats and dragons? Hmmm, must be from reading Peter Grant’s stories about cats and firearms (or spilled ammo). Yeah, that’s gotta be what your subconscious was channeling. 😉

  3. Um, a minor but perhaps significant quibble: Juries can’t demand anything. Once I was on a jury where we asked for a specific type of dictionary. We were refused because it was not part of admitted evidence. The ones demanding DNA evidence are prosecutors and maybe defense attorneys, who may or may not understand it, or may think they can present it as absolute proof or absolution to the jurors. Really, the way a judge charges the jury, you’re cut off from all but what is presented in court.

    What might be fun for those with the know-how is to have someone who’s taken courses in forensics but took another path in life get caught on a jury for a murder trial. He can only look at the evidence as presented, but nothing keeps him from accessing what’s in his head. And some of it doesn’t square with the testimony and evidence. What can he do with just the testimony and evidence that was presented in court?

    1. Good point, and yes, demand is probably too strong a word – but two instructors, former and serving LEO, have said pretty much just that.

      The story idea is a good one.

      1. It comes to whether that expectation of forensic evidence and a full confession has served to move the fulcrum of reasonable doubt. It may not be a demand but moving that target in their mind

    2. I think her point with the ‘juries demand’ was along the lines of ‘The CSI Effect’ (which had other names before) where the juries (some of them anyway) don’t think there is a strong case _unless_ there is DNA evidence.

  4. One interesting thing in a science fiction story would be the effect of widespread human cloning. I haven’t had it come up in the Gus on the Moon universe yet, but I could completely see a story in which a lab tech says, “I can only tell you the DNA is from a Shep. No, not a German Shepherd Dog. A clone of Alan Shepard.”

    In a world like the game Eclipse Phase, where the body is a sheath and changeable at will, your investigators would have the further complication of trying to determine whether the ego currently in the body was the ego driving it at at the time of the crime, or if the actual culprit egocast off to some distant location and downloaded some poor infomorph into the body as a fall guy.

      1. I was wondering, do they cover the issue of fabrication of DNA evidence in your classes? Or would that be a different subject? I’m referring to this: and this: I was pretty shocked/concerned when I read those articles a while back, and I was wondering if maybe since then new techniques have been developed to detect (assuming such a thing is even possible to detect) that sort of thing. Again, I’m *loving* this series! 🙂

        1. We have not covered it – although I’m going to send these links on to my prof – but this isn’t surprising. I could, given time and material, do either of them. But this goes back to the ‘most criminals are uneducated and unskilled’ point. Which is why we writers love to take criminals that have the background to maybe carry this off, and run with them. I will say that getting the supplies to create the ssnps (short bits to replicate the loci) would be expensive and traceable. A PCR thermocycler itself is a non-trivial piece of equipment. Writing science fiction, though…

          Have you seen the articles where they are embedding imagery in DNA? Perhaps we’ll have to tag ourselves to prove that we are the real us, in the future. Hacking clones would be… interesting.

      2. Huh…my reply didn’t show up. It had a couple links in it, so maybe that’s the issue?

    1. They used that as the basis for some crime drama (I want to say CSI:NY) – “our heroes” think they’re on the trail of a serial killer, only to ultimately discover somebody at the factory for the cotton swabs (or something like that) had accidentally contaminated on them somehow.

      1. And if there was a twist ending to this one, the person actually would have been the criminal…

      2. Yep, it was CSI: New York. I know the episode. new York is the only one that I still watch, and that is for Gary, not the science.

        1. Indeed. I’m not an expert, but I’ve caught some howlers. Hence the term I’ve coined: “CSI-ence fiction”.

          1. I wonder, is that akin to Anne Science? (a term used by DRoP fans when faced with weird science (or lack there of) in the series)

  5. Possible trivia useful for writers… If someone has done military service since about 1991 their DNA sample is available to law enforcement (with a court order.)

      1. Yes, and it says right there on your Social Security card that the number is for Social Security purposes ONLY, and no other use is authorized or legal.

        “Military DNA can only be used for identification” falls into that same category. That’s what they PROMISED – but that’s not how they’ll use it.

      2. From the National Defense Authorization Act of 2003:
        Ҥ 1565a. DNA samples maintained for identification of human remains: use for law enforcement purposes

        (a) Compliance with a court order.

        (1) Subject to paragraph (2), if a valid order of a Federal court (or military judge) so requires, an element of the Department of Defense that maintains a repository of DNA samples for the purpose of identification of human remains shall make available, for the purpose specified in subsection (b), such DNA samples on such terms and conditions as such court (or military judge) directs.
        (2) A DNA sample with respect to an individual shall be provided under paragraph
        (1) in a manner that does not compromise the ability of the Department of Defense to maintain a sample with respect to that individual for the purpose of identification of human remains.

        (b) Covered purpose. The purpose referred to in subsection (a) is the purpose of an investigation or prosecution of a felony, or any sexual offense, for which no other source of DNA information is reasonably available.
        (c) Definition. In this section, the term “DNA sample” has the meaning given such term in section 1565(c) of this title. “

  6. I read somewhere that one possible forensic countermeasure would consist of emptying a vacuum cleaner bag onto the crime scene. This would work better if you could scoop dust out of, say, a hotel maid’s vacuum cleaner, or raid a vacuum cleaner used to vacuum up after a department store closes for the night.
    The good news would be most criminals don’t prepare in advance.

  7. Over the past couple of years, I’ve assisted some folks from a university in Denver on a project. They were collecting samples of water from the distribution system in order to test a procedure for characterizing every organism living in the water by massively testing DNA.
    They’re getting to where they can detect every species of bacterium in a presence/absence fashion, and they may be able to quantify each species by the quantity of particular DNA and RNA sequences.
    (Yes, they were sampling drinking water. The water department doesn’t guarantee sterility; it guarantees an absence of coliform bacteria which are indicators of the possible presence of pathogens.)

    1. Part of the metagenomic project. The maths and algorithms behind that, and the computing power, are awe-inspiring. Beyond me, for sure. I’m taking a Bioinformatics class this semester and we touched on it. It’s very impressive.

  8. “Above and beyond the implications of this, are the growing privately held databases of DNA that are being created for genealogy purposes. What if your investigator is given access to one of those? I’m sure there are contracts between the company and the individuals who send in their samples to be told how much of a Neanderthal they are… surely there is some kind of privacy shield in place.”

    And one of them has already violated the agreement, if what I heard last year is correct.

    So much for the agreement.

    And that is one reason why I refuse to take their test. Never mind that I already know most of my genetic make-up. With names like Murphy, (changed from Murffee back in 1700’s) in the family it’s kinda easy to figure out.

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