In this Dec. 27, 2016 photo, a filter disc contaminated with blood samples by flies similar to the ones, left, raised by David Rivers, Ph.D., Loyola University biology department chair, for his research in Baltimore, Md.. Rivers and his students are researching on how to help law enforcement to identify real blood stains from fly contaminants at crime scenes. (Kenneth K. Lam/The Baltimore Sun via AP)
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