Becoming a Crime Scene Investigator by Jacqueline Detwiler-George

Author:Jacqueline Detwiler-George
Language: eng
Format: epub
Publisher: Simon & Schuster
Published: 2021-04-20T00:00:00+00:00

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IN A CONFERENCE ROOM in the Baltimore Police Department, Sean Dorr draws a fingerprint on a sheet of my notebook paper, a series of parallel arches with splits and spurs heading off them. “There are three basic types of friction ridge details,” he says. Dots are directionless units that appear as a blip on the lift card. Ending ridges flow until they come to an abrupt stop at something else. Bifurcations are just what they sound like: ridges that split into two or more pieces.

These details are what analysts are comparing when they look at fingerprints—not necessarily whether you’ve got whorls or arches or loops, which are just general categories, but whether the spatial arrangement of the peculiar minutiae in two prints cannot be explained by anything but sameness. Fingerprints from crime scenes don’t come in neat and orderly, after all. They arrive in several ways: as photographs from scenes; as photographs from the forensic bio unit; or, more often, on lift cards. The mobile unit produces the lift cards on scene, using a brush to swirl powdersI over hard surfaces, pressing clear tape on top, and attaching the lifted print to a card to preserve it in perpetuity. Under any of these circumstances, the prints might arrive smeared, skewed, or in pieces. You may only have a few ridges to focus on, and in that case you’ve got to hope you can find enough quirky patterns to reach a quorum.

Friction skin analysts perform their intricate work under quiet, library-like conditions: Next to a shelf of favorite reference books, say. Under a particular lamp. Dorr uses a five-dollar, adjustable-neck LED lamp from Target that he angles at precisely 30 degrees so the light hits the prints from the side. He slides the prints, on cardstock, under a pair of 5x magnifiers with spindly legs so that light can pass through underneath. Five times is about as high as he’ll go on magnification: any more and the distortion and background noise gets overwhelming.

Dorr compares fingerprints the same way you’d sink into a lake. First, he determines what he’s looking at—a finger? A palm? He orients the print—left hand, right hand, up, down. Slots it into a category of arch, whorl, or loop. Then he slides lower to observe the details, keeping track of them with a little metal pointer. One specific feature, or a grouping of them. His favorites are combinations, when dots, ending ridges, or bifurcations occur next to or on top of each other. Take the little Parisian island on my middle finger. That’s an enclosure, two bifurcations aimed at each other like this [lt][gt]. A great place to start.

From the initial feature or group, Dorr moves out like a ripple, finding, grabbing, and adding other details to establish an overall pattern. There might be a hundred features in a print, the majority of them ending ridges. The second you find something in one print that doesn’t appear in the other, you exclude that person from having committed the crime.

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