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INVESTIGATIONS 24 Law Enforcement Technology November 2014 www.officer.com and snow is a great place to gather them. "It's one of the most challenging sur- faces yet it is a great opportunity to have evidence," explains Lesley Hammer, Forensic Examiner, Hammer Forensics. "When it snows you get a fresh surface. It's like a blank canvas." Other surfaces such as gravel don't leave the same quan- tity or quality of impressions. "It's dif- ficult in snow to not leave an impression," she says. Regardless, snow does come with its own set of challenges. Snow complications "Snow has its own challenges in a bunch of different areas," explains Wolfe. For example, snow is transient. Even in areas where several feet exist, snow comes and it goes. At any moment a footwear or tire track impression can melt or be filled with more snow. Another challenge is the weather itself. "It's pretty inclem- ent," states Wolfe. "It's cold and (officers) don't want to spend a lot of time outside photographing and casting impressions." Hammer agrees, explaining she's often collecting impressions in temperatures ranging from 20 to 40 below zero. Another challenge is snow's consis- tency and color. "We talk about snow transforming," says Wolfe. "There are different types of snow ranging from real fine grain melting snow to coarse grain non-melting snow, and this may affect how you photograph and how you cast the impression. Color also complicates a snowy scene. "It can be more difficult to photograph because it's white, but also it reflects," says Wolfe. "You're trying to photograph something that is made up of clear particles. You get small mirrors reflecting back at you." In winter, a lot of flat white without contrast complicates the location and documenta- tion of snow impressions. Lighting and coating techniques have to be used to bring up the contrast, explains Wolfe. Recognizing and locating When responding to a crime scene in snow, officers need to be thinking about what trace evidence might be present even before they arrive. Understand you might drive right over the evidence, explains Hammer. Investigators should ask themselves, "What impression might be part of the scene versus part of the first responder effort and protect those," says Hammer. Once on-scene, all the photog- raphy and casting needs to be determined quickly because of snow's transient nature. "They really need to be evaluated right away," Hammer explains. "(Snow impressions need to be) prioritized in the other evidence." Finding the tracks is important not only to place a suspect at the scene, but they can also lead officers to a suspect. "I had a series of burglaries and the same set of shoe impressions kept showing up in the snow," says Hammer. "I've been involved in several cases where not just the impression, but the track of the impression assisted. The officer could follow someone right to their home. In Photography should be utilized along with casting. Sulfur cement is another common casting method, although need for additional equipment and the smell are disadvantages.