Trace Evidence of an Author: Point of View, Purpose, and Voice
In many ways, Locard’s Exchange Principle is the bedrock of modern forensic science. According to Locard, when two things come into contact with each other, like a suspect and a crime scene, they transfer materials. This explains why a suspect leaves behind trace evidence like fingerprints, hair, and fibers from their clothes while picking up tell-tale mud on their boots.
When we write, a similar exchange takes place. As authors, we leave fingerprints all over our work, especially in the purpose we choose, the point of view we take, and the voice we pick. Don’t believe me? Grab your tweezers and magnifying glass and let’s analyze the evidence.
Author’s purpose and point of view
The first, and perhaps, obvious way writers leave traces of themselves is through their purpose and point of view. Two authors writing about the same subject may have different purposes. The first may want to persuade you, while the other wants to inform. Even if two authors have the same purpose, their approach to the subject (in other words, their point of view) is as unique as their DNA. This includes what facts they choose to include or leave out and the conclusions they draw from the evidence.
Let’s take a closer look: This month’s book list features two books about the discovery of the Kennewick Man, a 9,000-year-old skeleton found on the banks of the Columbia River in Washington: MYSTERIOUS BONES by Katherine Kirkpatrick (illustrated by Emma Stevenson) and THEIR SKELETONS SPEAK by Sally M. Walker and Douglas W. Owsley. 
As an exercise, read the jacket flap copy and study the table of contents for each book. What does each tell you about the author’s purpose and point of view? Do the authors cover exactly the same topics or do you see a difference? Do you think their purpose and points of view are the same? If not, how do you think they will differ? Does one point of view more closely match your own?
Voice
Authors also leave traces of themselves in terms of the voice they choose for a piece of writing. Is the voice humorous? Poetic? Energetic? Formal? Informal? The voice should help the author 
achieve their purpose and communicate their point of view. 
Try this activity: Compare a paragraph from MORE ONE-HOUR MYSTERIES (Mary Ann Carr) with Carla Mooney’s FORENSICS: UNCOVER THE SCIENCE AND TECHNOLOGY OF CRIME SCENE INVESTIGATION. How would you label the voice of each? What elements of the writing led you to that choice? Hint: Look at things like word choice, punctuation, length of sentences. More informal or humorous voice might rely on shorter sentences, more exclamation points, and more informal language.
Your Author Fingerprints
Now, look at a piece of your own nonfiction writing. What’s your purpose and point of view? How would you describe your voice? Why? Is your voice a good match for your purpose and point of view? If not, pick another voice and revise your work.
And don’t forget, Locard’s Exchange Principle is a two-way street. Even if a piece of writing doesn’t work out the first time, every time we write we pick up new skills. That means all our writing leaves its imprint on us, helping us develop and grow as writers.
Kirsten W. Larson used to work with rocket scientists at NASA. Now she writes books for curious kids. She’s the author of WOOD, WIRE, WINGS: EMMA LILIAN TODD INVENTS AN AIRPLANE, illustrated by Tracy Subisak (Calkins Creek, February 2020), CECILIA PAYNE: MAKING OF A STAR (SCIENTIST), illustrated by Katherine Roy (Chronicle, Fall 2021), along with 25 other nonfiction books for kids. Find her at kirsten-w-larson.com or on Twitter/Instagram @KirstenWLarson.
THE O.O.L.F. FILES
This month, the Out Of Left Field (O.O.L.F.) Files provides links to learn more about forensic science, voice choice, and much more.
- Learn more about Locard’s Exchange Principle at Science Struck.
- The Crime Museum is another fun place to explore Locard’s Exchange Principle and related topics.
- Need some help deciphering voice? Melissa Stewart has one of the best videos around about The Voice Choice in writing.
- Looking for some online brain teasers and mysteries for your students? Check out Squigly’s Playhouse.
- One-Stop English has a fun “murder in the classroom” mystery activity for students.
Carla Mooney loves to explore the world around us and discover the details about how it works. An award-winning author of numerous nonfiction science books for kids and teens, she hopes to spark a healthy curiosity and love of science in today’s young people. She lives in Pennsylvania with her husband, three kids, and dog. When not writing, she can often be spotted at a hockey rink for one of her kids’ games. Find her at 
Sue Heavenrich writes about science for children and their families, from space to backyard ecology. Bees, flies, squirrel behavior—things she observes in her neighborhood and around her home—inspire her writing. A long line of ants marching across the kitchen counter generated one of her first articles for kids. When not writing, you can find her committing acts of science from counting native pollinators to monitoring water quality of the local watershed. Her most recent book is Diet for a Changing Climate (2018).
Maria is a children’s author, blogger, and poet passionate about making nature and reading fun for children. She’s been a Cybils Award judge since 2017 and a judge for the #50PreciousWords competition since its inception. Two of her poems are published in The Best Of Today’s Little Ditty 2016 and 2014-2015 anthologies. When not writing, or reading, she bird watches, travels the world, bakes, and hikes. Visit her at 