Flags planted by students of an FBI training course identify the boundaries of a potential burial site. (Photo: Courtesy of the FBI)

Killers have a race against the clock to hide the remains of their victims. They have to find a place off major roads, with ground relatively easy to dig—a spot quick to access and escape from, and one that is not likely to be seen from above.

The search for clandestine graves in open terrain means investigators have very little go on to determine where certain killers may have concealed their victims. For decades some agencies have used the “traffic-light system” (Red-Amber-Green, or RAG, system) by which the areas that may be of most interest to searchers are color-coded on a map, with red being the best hiding spots for remains.

Now an Italian team has refined a method of incorporating yet more desired factors into a GIS system, which could narrow searches further based on whether graves were dug during the day or at night—and find the most crucial evidence of all in homicides, they report in the Journal of Forensic Sciences.

“In contrast to previous studies, a new GIS-based method, based on cross-referenced RAG maps in order to evaluate ‘cumulative’ suitability to host a burial, was reported,” the scientists write. “The goal of this technical note was to thoroughly illustrate this innovative GIS-based presearch method for demonstrating that it can assist investigators as well as canine scent detections team(s) with better management of efforts, resources, and time during recent clandestine grave ground searches.”

The seven factors that went into their RAG mapping were: the search area access and exit prospects; the “diggability” of the ground; the slope of the landscape; the sparseness of the vegetation; the absence or presence of human-made structures; the stability of the geomorphology of the area; and the potential visibility of the act of digging at the locations, they report.

Favored by far were soil that was soft and with easy “diggability,” less than 20 degrees of slope, a spot devoid of both vegetation and human structures, stable ground not affected by water, and locations not visible by other people, they explain.

The team, led by Roberta Somma of Università degli Studi di Messina, then tested their methodology with “blind” tests.

At two sites in northeastern Sicily, “killers” buried two mannequins at simulated crime scenes far from prying eyes: one in an area cultivated with olive trees, and another in a sheltered area near a lake.

Nine students searched for the bodies.

At the olive grove near Ali, the “body” was buried in August 2015, and the search started six weeks later. The searchers were given a 40-square-kilometer search area. Using the digital surface models (DSMs), the red areas of most interest narrowed the landscape to about 5 percent of the total area.

At the rural area near the lake in Messina, the “body" was buried in May 2017, and sought by the student team about six weeks later, with a given search area of about 16 square kilometers. The red area using their method focused searches on about 2 percent of the terrain.

Both bodies were found within the area defined as red by the DSMs (which accounts for more suitability factors). At the olive grove, the mannequin was found in about an hour. Near the lake, it was located in approximately three hours.

The DSMs were more effective in scoring the map areas and guiding the search party, they write, because the additional factors account for more careful daylight burials, they write.

“If the culprit conceals the body in daylight and worries about the possibility of being seen by eyewitnesses, then the DSM scenario will be the most appropriate,” they write. “Nevertheless, at both crime scenes, the time spent for the ground search is an outstanding result because without the application of this method it would have been impossible to spot the clandestine graves in such as a short time, giving the specific features of the territory.”

Searches for clandestine graves have always been a major hurdle for detectives in the hunt for killers trying to cover their tracks. The textbook Practical Homicide Investigation by Vernon Geberth suggests considering the nature of the killing, whether it took place in a different location, and then using a series of tools to narrow down a search area, including aircraft searches, thermal infrared thermography, ground-penetrating radar, trained cadaver dogs, search by foot, probing with a steel rod, and use of a vapor detector to determine decomposition gases from a corpse.