Crime Scenes for Writers: DNA and Biologics

Here we are at the last post in the series. Time flies, right?

Most of us are familiar with DNA, the individual blueprint for each of us. DNA testing has come so incredibly far in the last twenty years, almost to the point that we expect DNA to answer most if not all of our questions. That makes CAN an interesting place for writers to stymie the investigator (and the reader).

DNA is a powerful tool, yes, but not without exception in the field of criminal investigation. Consider the following scenario:

The Case of Sally Simms

Sally lives alone in her apartment. In the last three days, she’s had new appliances installed, new cable run for the internet, her boyfriend has visited several times, her sister and her sister’s boyfriend were over for dinner, and she had a coworker over for coffee.

Sally is found dead on the floor of her hallway. The science teams go through her apartment collecting everything they can find and Sally goes off to the autopsy table. The police begin with the list of possible suspects: Sally’s boyfriend, sister, sister’s boyfriend, the appliance installer, the cable installer, and the coworker.

DNA is everywhere. Each person in the apartment left their DNA behind. If Sally’s cause of death was a blow to the head, DNA is not helpful unless the object is found and DNA is recovered from parts of the object only the killer would have touched. Your police detective must turn to other investigative means.

During autopsy, should DNA from seminal fluid be found to match both the boyfriend and the sister’s boyfriend, Sally’s sister is going to want an explanation, but it doesn’t make either of them the killer, especially as Sally was dressed and in the hallway. Scrapings from under Sally’s fingernails might yield DNA, but if the suspect shows a scratch healed beyond the time frame of her murder, it might just mean Sally didn’t scrub her hands or under her nails.

Plausible DNA

Now, in most cases, DNA is eliminated because it has a plausible reason for being where it is. If other lines of investigation develop a suspect, DNA might support it, but not be conclusive. I don’t know about you, but I get a perverse kick out of writing crime stories in which DNA is not a major part of evidence, just because I can and I like the unexpected.

DNA is absolutely helpful in the case of serial crimes such as rape and murder, since unknown DNA from crime scenes is entered into and checked against CODIS, the Combined DNA Index. Once a suspect’s DNA is available for match, he or she could be connected to a series of crimes.

DNA can be collected from almost any surface and from almost any body fluid. Hair won’t give DNA but the hair root (if torn out) can. Naturally shed skin won’t give you much, but scrape your arm across an abrasive surface and it’s possible.  And when stranger DNA is present from a person who has no explanation for being at the location, good chances are you have your criminal.

Biologics

But there’s more. In recent years, we’ve made serious headway into biologics which, in addition to DNA and fingerprints, also includes palm prints, palm vein patterns, facial recognition, ear recognition (mostly in Europe still), Iris patterns, retina recognition, hand geometry, and odor or scent.

What was partially developed for security has become a database of biometric information. The Department of Homeland Security has IDENT, which includes biometric and associated biographic information. The Department of Defense has ABIS, the Automated Biometric Information System. CODIS, which also includes the National DNA Index, will, I suspect, branch into biometrics if it hasn’t already.

We already use biometrics to solve a crime such as Sally’s. Even if the killer wore gloves, should a lamp base or makeshift weapon turn up in good condition, it would be possible to match the size and shape of the hand to the person who wielded it. If her building has solid security camera coverage, facial recognition might identify or confirm a suspect entering and leaving the building near the time of the murder.

The Future is (Mostly) Now

The possibilities are as numerous as the writer’s imagined scenarios.  Consider shifting the story ten years into the future, and the writer could have a lot of fun with solving Sally’s murder.

I hope this series has been helpful. I’ve been working on a series titled Body of Evidence, but I’m not certain you would be interested in reading about the evidence a body can yield after death. Please comment below if you’d like me to post the Body of Evidence series. Though it’s not written in graphic language, some of the subject matter may prove uncomfortable for some readers.


Has anything in this series changed the way you look at criminal investigation from a storyteller’s point of view?

Other posts in this series:

Crime Scenes for Writers: Introduction

Crime Scenes for Writers: Reading the Scene

Crime Scenes for Writers: Fingerprints

Crime Scenes for Writers: Blood Evidence

Crime Scenes for Writers: Ballistics

Crime Scenes for Writers: Trace

Crime Scenes for Writers: DNA and  Biologics

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Crime Scenes for Writers: Trace Evidence

Using trace evidence to solve the crime in your story is a great way to delay the payoff and finger the guilty party. I’ve given a list of the most common types of trace evidence and a brief description of each, though they could all be a post on their own.

Fiber

Clothing, leather, car interiors, carpet, and rope can all provide fibers for the investigators to discover and trace. The Mass Spectrometer is one tool used to identify the chemical makeup of a fiber. For example, carpet manufacturers’ and some fabric manufacturers’ product chemical signatures are in a database or researchable. This could narrow down the year, make, and model in the case of a car, or distribution information in the case of carpet and other fibers.  The most common use of fibers, however, is to match them from the crime scene to the suspect or the suspect’s environment.

Plant

Plants have DNA just like we do, so seeds or pods can often be linked to a specific plant. This might tell investigators where the suspect or the victim spent time as plants are often geographically specific.  Another use would be, for example, the discovery of seed pods in the suspect’s vehicle and matching them to the seed pods under the victim.

Insect

Larvae and living insects aren’t considered trace evidence, but webs, egg casings, insect parts, and evidence of bites or stings can yield evidence as to location, length of time the victim was at the dump site or crime scene, and even season if the crime occurred well before discover.

Hair

Humans and animals shed hair all the time, making hair one of the most common types of trace evidence. Once a suspect is identified, strands of hair can be matched. If the hair is pulled from the root, it may contain enough biological material to get a DNA sample. Pet hair found on or near the victim and also in the suspect’s environment (matched to a specific animal) can also boost the prosecutor’s case.

Fluids

Fluids include bodily secretions, of course, but other fluids include tree sap, cleaning products, chemicals, beverages, oil and gas, and water (pond water, ocean water, etc.). While these give information about the crime, I’ve always thought it would be interesting to use a fluid as the breakthrough piece of evidence. Something totally out of place would stump investigators and extend the tension of the story.

Particulates

I like this sort of evidence, and I’m intrigued about how to use particulates to good effect in a murder mystery. Here are four:

  • Paint: In addition to binding chemicals, paint often includes a mineral or metal as a color ingredient. These can be matched to known paint products, vehicles, and other elements of locations. In the world of crime shows, I’ve seen it most often used to identify a vehicle, but wouldn’t it be fun to connect it to an artist’s studio or the statue in the town square?
  • Soil: The great thing about soil is that it’s fairly localized depending on the particulates. Sandy, clay-based, loam, fertilized, mineral-rich . . . all give the investigators information they might not otherwise discover.
  • Metals: Paint, vehicles, tools, clothing fasteners, soil, weapons, and much more, contain metals that can be traced and/or matched to the crime scene, dump site, or suspect’s environment. We see it used most often to identify, again, a vehicle, but flecks of gold might indicate a manufacturing process, and copper shavings might point to the plumbing or construction industry.

Trace evidence offers so many opportunities for the writer and suspense for the reader. It’s by far my favorite type of evidence to include in stories.

The last post in the series is DNA and Biologics. See you then!


How many ways can you think of to stump the reader and detective with trace evidence?

 

Other posts in this series:

Crime Scenes for Writers: Introduction

Crime Scenes for Writers: Reading the Scene

Crime Scenes for Writers: Fingerprints

Crime Scenes for Writers: Blood Evidence

Crime Scenes for Writers: Ballistics

Crime Scenes for Writers: Trace

Crime Scenes for Writers: DNA and  Biologics

Crime Scenes for Writers: Ballistics

muzzle-1080231_640Ballistics is one of the older forensic sciences. As far back as the early/mid 1800s, bullets could be matched to a particular caliber of weapon. However, it wasn’t until 1895, after rifling was introduced, that ballistics came into its own. Improvements in microscope photography and the introduction of the electron microscope in the 1970s brought the forensics of guns into the modern era.

However, there are two problems with using ballistic evidence. The first is that some bullets fragment on impact. Forensic scientists need enough fragments to reproduce an image of the bullet. If they don’t have them, the bullet is of little help. The second is that, in order to compare a bullet from a crime scene to a bullet from a particular gun, the lab people need the gun. No gun, no comparison, though the bullet may be matched to other crime scenes through NIBIN/IBIS (National Integrated Ballistic Information Network).

Guns, when recovered, can yield significant information including biologics and fingerprints. I’m guessing that’s why so many murder weapons end up buried or tossed into deep water. 🙂

Other elements of investigation include the trajectory of the bullet, the velocity, if it can be determined, and the presence of gun powder residue, either on the suspect’s hands or near the victim’s wound (we’re already familiar with the term “stippling” from TV, which indicates the gun was in close proximity to the victim when fired.

Recovered suspected weapons are fired into a water tank. The bullet is removed from the tank and compared to any bullets or fragments found at the crime scene. Rifling marks, the lands and grooves, are individual to each gun. There may also be indicators of speed of rotation as the bullet passes through the barrel, and/or marks from the firing pin. Criminals who bench-load their own ammo probably leave tooling marks and individual elements in their gun powder as well.

I was happy to see a show this past year in which a detective explained to a gang member exactly why holding the gun sideways gangsta-style was a bad idea. The kid didn’t listen and the gun ejected the shell into his face. It brings to mind the fact that investigators can tell a lot about the gun and the position of the shooter by where the shell casings end up.

Speaking of shells, we’re also familiar with the term “policing the brass,” which indicates the shooter picked up his spent shells and took them with him. Most shooters don’t take the time, possibly leaving behind prints or other information with the casings themselves. I had some first-hand experience due to an unruly neighbor. My husband and I got a mini-lesson in trajectory and helped locate the casings. Each was picked up with care and stored in evidence. That’s why I own a revolver. (Just kidding . . . about the why, not the revolver.)

This doesn’t just refer to guns, but one thing TV routinely gets wrong is the use of plastic bags for evidence. Most evidence is collected in paper bags. Guns may be put into a paper bag or wrapped in brown paper. Paper preserves the evidence that plastic might easily destroy.

Several great sites exist for writers who want to know more about ballistics and guns in general to create accuracy in their stories. For examples, the NSSF published The Writer’s Guide to Firearms & Ammunition as a pdf download. But my favorite of all time and my go-to for questions is Lee Lofland at The Graveyard Shift. If you are at all interested in writing crime stories, his site should be your first bookmark.

Next week is trace evidence.


 

Do you find ballistics evidence an interesting part of the story or less so? If not your favorite, do you think it’s because we’re more familiar with it?

Other posts in this series:

Crime Scenes for Writers: Introduction

Crime Scenes for Writers: Reading the Scene

Crime Scenes for Writers: Fingerprints

Crime Scenes for Writers: Blood Evidence

Crime Scenes for Writers: Ballistics

Crime Scenes for Writers: Trace

Crime Scenes for Writers: DNA and  Biologics

Crime Scenes for Writers: Blood Evidence

This type of evidence is often misrepresented on television. How many times have you seen a murder victim lying in a pool of blood on a TV show? These victims are usually in a thick, glossy, bright red liquid pool, right?

Not so much.

Pools of any depth begin to separate. Thin layers of blood tend to dry quickly and become dark brown. These TV victims would realistically be lying in dried, sticky brown stuff or in a sticky mess of separated plasma and browning goo. It may be one of the forensic elements on TV shows that irritates me most, but I’ll get off my soap box now.

Blood is a fascinating substance. It’s three to four times thicker than water. It has a metallic scent and taste. And it’s something we’ve all seen at some point. This “liquid life” also carries with it evidence of poison in many cases, our DNA, information about our health, our blood type, and sometimes our state of mind (adrenaline and cortisol). We’ve used the ABO blood group typing system since about 1930. It was, before DNA, what we used to eliminate possible suspects from crime scenes.

Beyond type and content, how blood is left at the crime scene gives great details about what occurred. For example, blood may be dripped, transferred, or splattered.

Dripped blood is passive, dropped in a round or elliptical pattern depending on whether the bleeding person is standing still, moving slowly, or moving fast. Read by a knowledgeable investigator, direction and rate of movement become clear.

Transfer happens when, say, a hand or sleeve comes in contact with blood and then touches another surface such as a wall or towel. If both parties have been injured (not uncommon in stabbings), their blood may mix before transfer.

Spatter is the sexy part of blood evidence for most people interested in forensics. Spatter comes in three types: low, medium, and high velocity.

Low velocity spatter is often “cast off,” or flung from an object used to strike or stab the victim. Imagine shaking water from your hands to get the idea.

Medium velocity spatter leaves larger patterns, such as arterial spray or blood erupting from the wound when struck.

High velocity spatter is a fine mist and generally caused by bullets.

The pattern of blood spatter, including voids in spatter that may mark the location of the perpetrator, reveals such things as the attacker’s height, left or right handedness, where they were positioned, and possibly how hard the victim was struck. It may also reveal the type of weapon (independent of the wounds), height, strength, and angle of the blows.

Blood is corrosive and really soaks into things. Even with a good scrubbing, traces will remain on most surfaces. It can be painted over, smeared with cleaners, even removed from the naked eye, but it cannot be eradicated completely unless you care to replace every element of the room including those floor joists.

To assist crime scene technicians in uncovering evidence of blood, the traditional method of luminal is used in conjunction with a black light.  These days, lasers are used in some cases and a new forensic camera will eventually replace luminal all together.

Beyond walls, carpet, and furniture, blood can end up in the smallest of nooks and crannies: behind unsealed baseboards, the undersides of lamp shades, on the ceiling across the room. In one case blood,  absorbed through carpet and subfloor(both of which were replaced), only to be discovered along the floor joist. It’s been found in sink drains and plumbing pipes, in soil and on plants, under furniture, in the tiny screws of eyeglasses, between a cleaned knife’s hilt and blade, and even inside the tiniest cracks of a cell phone.

There’s one more thing blood can accomplish. It can, in court, “prove” murder or death if enough blood is present to show that life could not be sustained.

Blood evidence, to my mind, is fantastic for writers. We can hold the tension of lack of evidence and then reveal a whole crime scene with luminal. We can provide what appear to be inconsistencies for our characters to resolve. If set in history, a brilliant detective might use the budding technique of studying blood evidence to solve a crime that is otherwise unsolvable. And the finding of the tiniest speck of blood in the oddest of places can make a case the reader thought was lost.


How often have you seen blood evidence used to great effect in a novel? What was your reaction?

Crime Scenes for Writers: Introduction

Crime Scenes for Writers: Reading the Scene

Crime Scenes for Writers: Fingerprints

Crime Scenes for Writers: Blood Evidence

Crime Scenes for Writers: Ballistics

Crime Scenes for Writers: Trace

Crime Scenes for Writers: DNA and  Biologics

Crime Scenes for Writers: Fingerprints

I’ve been aware that my finger prints are in a federal database for twenty-five years. My husband often jokes that I couldn’t get away with theft or murder because of it. If you were ever employed by an SEC controlled business such as I was, or have worked in a daycare in the last fifteen years, your prints are on file as well.

As far back as 1684, academics lectured on the subject of finger prints. In 1788, Johan Mayer declared our finger prints to be individually unique, but it wasn’t until 1892 that finger prints were used successfully in a criminal prosecution. The man who testified, Juan Vusetech, created a classification of loops, whorls, and arches still used today.

I should interject here that ears, a long-used identifier in Europe, are just as unique as finger prints. However, technology is advanced enough for the matching of foot, toe, and elbow prints as well. Scientists can also match whole or partial palm and heel prints as well, as long as there’s a print with which to compare.

There are two types of finger prints that can be recovered from a crime scene. The first, patent prints, are visible to the naked eye. The second type, called latent prints, must be developed to become visible.

The technique of dusting (using a fine brush of powder above the print, not actually on it) and then lifting a print with tape has been in use since the early 1900s. We’ve come a long way from the black powder and tape method, though. These days there are light powders for dark surfaces, fluorescent powders for textured or multi-colored surfaces (used in conjunction with a black light), and more recently, a laser technique that illuminates the salt and other compounds on the skin’s surface to reveal a clear, photographable print.

For surfaces suspected of holding prints that can’t be raised by more conventional methods, there are two more weapons in the lab’s arsenal. The first involves exposing the surface to vaporized superglue to reveal the print. The second, which is often used only when nothing else works, involves fine gold particles in a metal vacuum to “paint” the prints for visibility. Inroads and successes have also been achieved in lifting prints from skin and porous surfaces.

There are a few limitations to using fingerprints to identify a subject. Since most murders are committed by someone known to the victim, prints are useless unless it can be proven that the suspect has never been at the crime scene or come into contact with the items found there. If the suspect has, for example, often visited his now deceased neighbor, his prints are meaningless to prosecution as they could have been left at any time (unless of course they are left in the victim’s blood). This is a great opportunity for the writer to implicate or draw attention away from a suspect character. If, for example, the reader knows the suspect has been in the house, or has not, but evidence is either to the contrary OR excluded, you ratchet up your reader’s tension.

The other problem with prints is that, while they are unique, they can be quite similar. Print experts use a point system for comparison. Computers are able to match more, but the eight-point match is the baseline. Further points must be matched to eliminate similar prints. It is a time-consuming process and often completed by hand, not computer.

Society is quite aware that finger prints are easily left and easily found, leading more criminals to use gloves. While an actual print can’t be recovered from a gloved hand, size and grip are often evident as the gloves leave something behind as well. And, should the criminal foolishly leave his gloves behind, the prints can be recovered from inside the gloves or on their surface (as part of the process of putting the gloves on).

Prints have been recovered from places people don’t normally think about such as the inside of a belt buckle, a shell casing, the sticky side of duct tape (even after soaking in river water), larger jewelry pieces, paper, faucets, and the undersides of tables, chairs, and countertops. Basically, anywhere someone might rest a finger, a print might be recovered, and the technology will only improve with time.

Because prints are so commonplace and well known to most of us, I think they are often overlooked by both writers and readers, which is a shame. It’s an old method jazzed up by new technology, but still not as sexy as DNA or sensational trace evidence. Still, in the right circumstances, all a jury needs is one single print to convict.


Where is the most unlikely or unusual place you can think of that might yield a finger print?

Crime Scenes for Writers: Introduction

Crime Scenes for Writers: Reading the Scene

Crime Scenes for Writers: Fingerprints

Crime Scenes for Writers: Blood Evidence

Crime Scenes for Writers: Ballistics

Crime Scenes for Writers: Trace

Crime Scenes for Writers: DNA and  Biologics