How a clump of moss helped convict grave robbers in Illinois | Science

It was a particularly heinous crime. Four workers at a cemetery near Chicago dug up more than 100 bodies and dumped the remains elsewhere in the grounds, in order 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 tiny clump of moss became crucial forensic evidence that helped convict grave robbers.

Dr. Matt von Konrat, head of botanical collections at the Field Museum in Chicago, became involved in the case in 2009 when he received a phone call from the FBI. “They asked me if I knew about moss and took the evidence to the museum,” he said.

An investigation by local police discovered human remains buried under just inches of earth in the cemetery, a site of enormous historical significance. Several prominent African Americans are buried at the cemetery, including Emmett Till, whose 1955 murder became a catalyst for the civil rights movement, and blues singer Dinah Washington.

Alongside the reburied remains, forensic scientists spotted various plants, including a finger-sized piece of moss. Hoping that this would help them solve the case, the FBI asked von Konrat to determine where the foam had come from and how long it had been there.

After examining the moss under a microscope and comparing it with dried specimens from the museum’s collection, scientists identified it as common moss, or Fissidens taxifolius. A survey at the cemetery revealed 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 dug up. The moss had obviously been moved with the bodies.

But when was the crime committed? The answer lay in a quirk of moss biology. “That’s the cool thing about moss,” von Konrat said. “When you’re dead, you’re dead, but with mosses it’s weird. Even when you might think they’re dead, they can still have an active metabolism.” Metabolism slowly declines over time as cells gradually die.

One way to measure the metabolism of moss is to bathe it in light and see how much is absorbed by the chlorophyll used to make food through photosynthesis, and how much light is re-emitted. Scientists carried out tests on moss found with the bodies, on a fresh clump from the cemetery and on 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 whole line of defense was that the crime had taken place before their employment. They were claiming that it had happened years and years earlier,” 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 the cemetery’s plant material was “key” to securing convictions when the case goes to trial.

Von Konrat, a fan of the BBC forensic series Silent Witness, never expected to work on a criminal case but now wants to highlight the importance of moss for forensic investigations. “I didn’t imagine we would use our science, our collections, in this way,” he said. “This highlights the importance of natural history collections. We never know how we might apply them in the future.”