A Lesson in Forensic Science for Writers

I got a brilliant idea for a psychological story about five years ago, right when I decided to take writing seriously and began pursuing it. The concept and characters thrilled me, right from the very beginning. Sitting down and writing my first draft really was the most fun I’d had in a long time. I didn’t want it to end, until I realized how much my facts didn’t add up. My excitement still held, but the new feeling of confusion on how much I didn’t know to make this book work, set in. What facts was I missing, you ask?

My forensic details.

Yes, I’ve read lots of mystery, psychological, and suspense books through the years, as they are my favorites. And countless shows have been watched, but was I really telling my story with concrete evidence, or would I confuse the reader even more with false information?


I started on my forensics research journey to make sure that what I was writing was legit. There are so many great books and conferences directed toward crime writers. (A few are California Crime Writers, Bouchercon, and Thrillerfest, but they are many more you can find online.) As far as book resources go, Writers Digest has a great selection. The ones I’ve most appreciated in guiding me to place the correct information in my stories, are the Howdunit books. There’s one on forensics, poisons, and police procedure and investigating. Each book has added the ingredients I needed to present a novel with much more backing because of my understanding on how certain situations occur, and how things realistically work relating to the crimes I present in my own stories.

I discovered there is a lot of misunderstanding behind the workings in forensic science.

For instance, D.P. Lyle wrote Forensics, A Guide for Writers. It’s where I get my gems of information. I want to share what he says in his book about the importance of fingerprints and how it can help your character solve a crime.

Fingerprints are individual to each person. No one shares the same print, not even identical twins. Our fingerprints never change from birth to death. They’re developed in utero. If you have deep tissue damage, or if someone shaves or burns off the pads of your fingers, the prints will disappear for a while, but once the skin repairs itself and the wounds heal, the print reappears. Severe damage involving the deeper layers of the skin, may have a permanent effect, keeping the print from reemerging. However, completely obliterating a print is difficult.

Basic Print Patterns: Arches, whorls, and loops are the basis for matching and fingerprint identification. We all have them, but how many and where they are located is unique. The patterns vary from person to person, but they vary from finger to finger in any given individual, giving us ten unique prints.


Locating and collecting fingerprints: Fingerprints are sometimes readily visible, while at other times they require a search. A print left in paint, blood, or grease on a wall will be much easier to find than one left on a trash bag by a hand not contaminated with any visible substance. There are three basic types.

  • Patent prints- are visible to the naked eye. They occur when the perpetrator of the crime gets a substance such as blood, ink, paint, dirt, or grease on their fingers and leaves behind a visible print.
  • Plastic prints– have a three dimensional quality and occur when the perpetrator impresses a print into a soft substance such as wax, putty, caulk, soap, or moist paint.
  • Latent prints-by definition, are invisible and can’t be seen without special lighting or processing.

Latent prints come from fingers that are contaminated with sweat and grime. Freshly washed hands will leave a fainter latent print. It is the job of the crime scene technicians and police to locate, expose, and collet these hidden prints.The best surfaces to search for latent prints are the murder weapon, any tools or objects left behind by the criminal, opened drawers or out-of-place furniture, and entry and exit points. Basically any spot the perpetrator may have touched. Both the plastic and patent prints can be easily photographed, and are visible so that the photo can be used for matching. Latent prints require special handling and the criminalist has a kit full of methods for collecting and exposing them.

Simple Inspection: To reveal latent prints, an angled light from a flashlight with or without aid of a magnifying glass may bring it into focus. Because of the oils of a latent print will fluoresce when exposed to some ultraviolet lights, these light sources may snap it into view. Other ways to grab a latent print are:

  • Print Powders– Fingerprint powders adhere to the moisture and the oils of the latent print residue and expose the pattern of the friction ridges. The powders come in a variety of colors and types. The chosen color should impart the greatest degree of contrast with the background surface. Black and gray are used most often, but white or another light color is used when the background is dark. They’re specialized powders as well. One being fluorescent. After it’s applied, the print will fluoresce under a laser light. Once the powdering process is complete, the print is photographed and “lifted.” Lifting is done by gently laying the sticky surface of a strip of transparent tape over the print. The print pattern sticks to the tape, which is then peeled away and placed on a card for later examination and matching.
  • Iodine Fuming– When heated in a fuming chamber, solid crystal iodine releases iodine vapors, which combine with the oils in the latent print to produce a brownish print. It must be photographed quickly, as the print fades.
  • Ninhydrin The object that holds the latent print is dipped in or sprayed with ninhydrin solution. The reaction of the ninhydrin with the oils of the print produces a purple-blue print. This process is very slow, taking several hours to appear. Heating the object hastens the reaction.
  • Silver Nitrate– When the latent print is exposed to this substance, the chloride of the salt molecules in the print residue reacts with the silver to form silver chloride. This colorless compound “develops” when exposed to ultraviolet light, revealing a black or reddish brown print.

Bloody Prints-Next time you want to put a blood stained finger print in your scene, first understand that latent or faint prints left can actually present a special problem. Often too faint to photograph and the powders may not expose them well enough. If this becomes a problem Luminol or Amido Black can help.

  • Luminol- It reacts with the blood’s hemoglobin, causing it to fluoresce when viewed in dark conditions. The glow doesn’t last long, so once the print’s exposed it must be photographed. Luminol reacts with very small traces of blood, even where none seem to exist. Scenes that are many years old or have been or painted over still hold traces of blood, and luminol will reveal them. Because it’s so sensitive in locating blood residue, it can also reconstruct a crime scene by uncovering a bloody trail.
  • Amido Black– it’s also known as Naphthalene blue black. It reacts with blood proteins and turns the bloody print a blue black color. The photograph is later examined for comparison.

Lastly we need to discuss the gloves. So many stories have the villain wearing gloves to make sure that their prints aren’t exposed all over the crime scene. Does they help?

Thin surgical-type gloves are sometimes so thin that the friction ridges still protrude and their pattern might be left on the smooth surface if the glove is contaminated with blood, grease, paint or some similar substance. Also, in some cases the perpetrator might have tossed the gloves after the incident, only to not realize that fingerprints from inside the glove can still be obtained.

Using leather or cloth gloves is no guarantee either. Though the person’s fingerprints are not left, the pattern of the glove fingerprints or palm might be. If the cloth glove has snags or the leather glove has scars or creases on the surface, this can leave a distinctive patterned print at the scene.

For more great details about all things forensics, check out D.P Lyle’s book!

Have fun writing your next crime novel and make sure to…I can’t quite put my finger on what I was going to say.


5e2ed-lauriLauri Schoenfeld’s first love is her little clan of three silly kidlets and her wonderful hubby, Andy. Writing is a close second. She began writing poems at the age of nine, and her love for literature and music developed into composing thirty songs. In 2014 her short story, Christmas Treasure, was featured in an anthology called, Angels from their Realms of Story. Her favorite genre to write is anything dark, psychological, and suspenseful, but she enjoys expanding her horizons and dipping her feet in other genres as well. Lauri teaches summer writing classes for kids and mentors teens throughout the year.She’s a Child Abuse and Scoliosis Survivor. Lauri runs a group for teen girls with Scoliosis called, The S Squad. Their motto is Strength, Support and Self Confidence. She’s been known to dance around the house with a spoon as her
microphone and sneak toppings from the ice cream bar. Lauri’s taken online classes at the Institute of Children’s Literature and was the President of the League of Utah Writers, Oquirrh Chapter for two years. She’s a member of Crime Writers and International Thriller Writers.