As dawn broke on a large Midwestern city in August, the partially clothed body of a young woman was found on a concrete slab near the state fairgrounds parking lot. The woman, in her early 20s, had sustained multiple stab wounds and some genital mutilation. Investigators found no traces of semen on site.
Though the fair had ended its 10-day run the night before and the parking lot had cleared of cars by 2 a.m., liquid blood and the body's condition led investigators to conclude a more recent time of death.
Police investigators were unable to discern any footprints on the concrete slab. But the parking lot, just 10 feet away from the body, was not paved; its surface was hard-packed dirt and took impressions well. At first, investigators thought someone driving a motor vehicle dumped the body in this location, but the amount of blood at the scene indicated the victim had bled out on the spot. Officials began a hunt for footprints in the parking lot and quickly found a pattern matching the sole of the victim's sneaker.
"We followed the footprint trail back to where the woman had entered the parking area," the police detective lieutenant reports. "From there, the paved road began and all traces were lost. But we knew that where the victim's tracks were found, the suspect's footprints also would be located, and the hard-packed dirt provided a good surface."
After locating and properly photographing all of the victim's footprints, investigators carefully measured the distance between the prints. The stride between the victim's left-foot and right-foot track measured an average of 26 inches when she entered the parking lot. But it was apparent from the track impressions that at one point she had looked over her left shoulder.
"The pattern in the bottom of the track was broken down, as if she had twisted her foot a slight amount," the lieutenant recalls. "We used a cleared area of the parking lot and attempted to reproduce the amount of twist. A female police officer, wearing a similar type of shoe, tried a variety of movements to duplicate the pattern of disturbance in the track. The same type of breakdown occurred when the officer looked over her left shoulder."
After the victim glanced over her shoulder, the distance between the footprints increased, first to 28, then 34 inches, indicating a boost in the speed of her walk. As the victim approached the far side of the lot, her stride grew to 40 inches.
A close inspection of the victim's individual tracks indicated that as her stride lengthened from 26 to 28 inches, the footprints showed more pressure being applied to the ball of the foot, but only enough to cause cracks in the soil. At 34 inches, the individual prints revealed the victim was now up on the balls of her feet, her heel marks gone. In short, she was running. Then her tracks suddenly exploded, kicking dirt 2 feet behind the prints as she went into an all-out sprint.
As investigators trailed the victim's tracks, they found another set of footprints. Because some of these prints overlaid a number of the victim's tracks, investigators determined these footprints most likely belonged to the perpetrator. Investigators then employed a procedure similar to that used to reconstruct the victim's actions to deduce the suspect's actions.
First, investigators photographed the trail and each suspect footprint using a tripod, footprint scale and offset lighting. Then they carefully measured the length of each clear footprint and plugged the average length into a formula designed to approximate the suspect's height. By measuring the perpetrator's stride, investigators presumed he also started out walking then broke into a fast run as he chased the young woman.