The press called her "Chicago's Woman Sherlock Holmes." Her publisher called her "The Mistress of Mysteries." It's a shame, really, that there isn't a chapter on Mary E. Holland in every anthology of Chicago history stories. Hers is one of those fantastic stories that fell through the cracks before anyone could really learn enough about her.
Mary was the assistant editor of Detective, a magazine for police officers, and did a lot of investigative work herself. She studied fingerprint sciences at Scotland Yard, then helped train law enforcement agencies in the United States, using dusting powders she invented herself. In 1910, she was one of the experts called to the stand in the first modern trial where a murderer was convicted based on prints.
Only bits and pieces of her work have come to light, most notably her notes on the "Bate Murder"—the first case in which a person was killed in a car. Billy Bate was found slumped over the steering wheel of a 1904 touring car; the man who hired it, "Mr. Dove," was gone without a trace. She examined the automobile and wrote up her notes for a Chicago paper.
“There exists in the blood stains on the automobile the unmistakable evidence that some person or some heavy object has been dragged from the rear seat over the right side of the machine,” she wrote. “This was done when the blood was warm. I cannot be mistaken in this. The hands of the person, whose finger prints still remain on the front portion of the machine and on the brass of the lamps, were dripping with blood." By analyzing the stains, the prints and the fibers left on the seat, she determined that there must have been a third person in the car.
Whether that claim is true or not remains unknown—the case was never solved. She wrote a fictionalized account of her involvement in the case as a part of a series of short detective stories she wrote towards the end of her life in 1913, some of which have recently been republished. You can read more on her life and career at the Mysterious Chicago blog.