Officials retraced the suspect's steps to determine where he entered the parking lot. The trail ended at a set of tire tracks. Several cigarette butts, all the same brand, were found in the area. Investigators believed the suspect sat in his vehicle, smoking, and lying in wait for his victim. They photographed and cast the tire marks and collected the cigarette butts for DNA analysis. Officials speculated the victim did not see the vehicle when she entered the lot, and later became aware of the suspect and began to walk fast, then run, and finally sprint.
Because of this diligent search for footprints, even though the body had been found on concrete, investigators developed a great deal of information and were able to reconstruct the chain of events leading up to the killing. They had photos and casts of the suspect's shoes, his approximate height, possibly his DNA, and, by using a computer program, an idea of the make and model of his vehicle.
Subsequent questioning of state fairgrounds workers led to a temporary worker, who smoked the same brand of cigarettes as those found and was approximately the determined height. His motor vehicle was parked in plain view outside his trailer, and the tires visually matched those found near the body. When questioned, the man supplied vague and evasive answers. Officers also observed the suspect's shoes and noted they had the same class characteristics of the footprints at the crime scene. They subsequently arrested the man, seized his shoes, and obtained a search warrant for his residence and vehicle. They found bloodstained clothing and a hunting knife stuffed in the air conditioner of the suspect's house trailer. He is now serving a life sentence.
"Because we were thinking of footprints right from the start, we were careful to avoid stepping on the best evidence we had," the lieutenant recalls. "We were fortunate to have a tracking surface we could use. If the crime had been committed on grass or in a wooded lot, we would have needed a more advanced set of skills."
While it's long been said that a picture tells a thousand words, to the crime investigator a footprint clearly does the same. Identifying and interpreting both victim and suspect tracks tells a story about the crime itself. Everything from the order of the events, the relative position of the people involved, the height of the individual and more can be learned by tracking footprints at the scene.
A crime is a dynamic, chaotic event that occurs in a three-dimensional space. But the crime scene investigator must reproduce the event by interpreting evidence found on two-dimensional surfaces, such as floors, ceilings and walls. When the crime occurs outdoors, the only surface available is often the ground. As the example above clearly denotes, experience and training in locating, documenting and interpreting footprints maximizes an officer's ability to reconstruct the crime and bring responsible parties to justice.
But not all surfaces where tracks may be found are created equal. Tracking on grass or forest debris is often more difficult than locating and interpreting footprints on dirt or snow.
When tracking footprints on grass or forest vegetation, first a careful search must be made at the crime scene and nearby for any disturbances that have changed the natural pattern of the plant life. Crushed leaves, bent stalks and plant material kicked up or pressed down are sought. Next, distinguishing between animal and human activity is achieved by determining the shape of the foot that made the disturbance. In North America, only humans and bears leave large flat tracks, and only humans wear hard-soled hunting boots. The final and the most difficult task is aging the track. This means determining to a reasonable degree of certainty when the footprint was laid. Many trails and woodlands in America are multiple-use and aging the footprints becomes critical in order to distinguish the suspect's footprint from all others. This type of tracking requires extensive training and experience, but the results are worth it.
"Broken or crushed vegetation can be aged," says Tony Kemnitz, former chief of police for the Mukwonago (Wisconsin) Police Department. "Moisture is squeezed out of a plant stepped on by a human shoe. The plant will appear a deeper green if recently crushed, then undergo a series of color changes related to the length of time since it was damaged."