It was a particularly heinous crime. Four workers at a cemetery near Chicago dug up more than 100 bodies and dumped the remains elsewhere on the grounds to resell the burial plots for profit.
Now, nearly two decades after the scandal broke at Burr Oak Cemetery in Alsip, Illinois, scientists have released details of how a small clump of moss became crucial forensic evidence that helped convict grave robbers.
Dr. Matt von Konrat, head of botanical collections at Chicago’s Field Museum, became involved in the case in 2009 when he received a phone call from the FBI. “They asked me if I knew about the moss and they took the evidence to the museum,” he said.
An investigation by local police found human remains buried under inches of soil in the cemetery, a place of enormous historical importance. Several prominent African Americans are buried in the cemetery, including Emmett Till, whose murder in 1955 became a catalyst for the civil rights movement, and blues singer Dinah Washington.
Next to the reburied remains, forensic specialists detected several plants, including a piece of moss the size of a fingertip. Hoping it would help them solve the case, the FBI asked von Konrat to find out where the moss came from and how long it had been there.
After examining the moss under a microscope and comparing it to dried specimens in the museum’s collection, the scientists identified it as common pocket moss, or Fissidens taxifolius. A study at the cemetery found that the species did not grow where the bodies were discovered, but was abundant in a lightly shaded area under some trees where police suspected the bodies had been unearthed. It was evident that the moss had been removed along with the corpses.
But when was the crime committed? The answer lies in a peculiarity of moss biology. “This is the good thing about moss,” von Konrat said. “When we’re dead, we’re dead, but with mosses, it’s strange. Even when we might think they’re dead, they can still have an active metabolism.” Metabolism slowly decreases over time as cells gradually die.
One way to measure the metabolism of moss is to bathe it in light and see how much chlorophyll, used to produce food through photosynthesis, is absorbed and how much light is re-emitted. The scientists carried out tests with moss found next to the bodies, with a fresh group from the cemetery and with other specimens from the museum’s collection.
“We concluded that the moss had been buried for less than 12 months and that was important because the defendant’s entire line of defense was that the crime took place before his employment. They argued that it happened years and years before,” von Konrat said. Details are published in Forensic Sciences Research.
Doug Seccombe, a former FBI agent who worked on the case and co-author of the study, said plant material from the cemetery was “key” to securing convictions when the case came to trial.
Von Konrat, a fan of BBC forensic science drama Silent Witness, never expected to work on a criminal case, but now wants to highlight how important mosses can be to forensic investigations. “I had no idea we would use our science, our collections, in this way,” he said. “This underlines how important natural history collections are. We never know how we might apply them in the future.”
