Here’s what you’ll learn when you read this story:

• When FBI officials wanted to find out who had exhumed human remains in a cemetery and reburied them to sell the plots, they consulted a botanist.
• Moss that had been buried along with the remains was examined to see whether it dated to the same time as the crime.
• It turned out that, despite claims to the contrary, the moss was there when the bodies were reburied, and the perpetrators were (spoiler alert) convicted.

Matt von Konrat, a botanist at the Field Museum in Chicago, has always been a fan of detective shows, but he never imagined that a phone call in 2009 would basically put him in his own episode of Law & Order.

When he picked up, it was the FBI—and they wanted to know if he could use his expertise with mosses to help them solve a grave-robbing case.

When agents arrived at the museum, they showed von Konrat a clump of Fissidens taxifolius moss that had been found in Burr Oak Cemetery in Alsip, Illinois. This moss, they believed, had been buried with the remains of three individuals who were illegally moved from their graves to another part of the cemetery by employees who thought they could profit off of selling the now-empty plots.

The FBI wanted von Konrat to identify what species of moss they'd found alongside the displaced bodies—and determine how long that moss had been underground.

“This investigation demonstrates how combining botanical identification and physiological experiments can yield crucial insights to assist forensic casework,” von Konrat said in a study recently published in the journal Forensic Sciences Research (appropriately titled “Silent witness: a moss provides important evidence in solving a cemetery crime”).

“It is clear that there is significant potential for bryophytes to be used within forensic science and that they, along with other plant material, especially microscopic, have possibly been underutilized.”

Mosses are bryophytes—a group of plants without roots that also includes hornworts and liverworts. Many bryophytes, which mostly go unnoticed, are very helpful to the environment, since they are able to grow even in sterile soils. By absorbing water and nutrients through hairlike rhizomes and releasing them back into the soil, they quietly form more soil that, in turn, allows the roots of new plants can take hold.

But there is also something peculiar about how mosses survive dry spells. Desiccated mosses still have active metabolisms, meaning that they can be rehydrated and (at least partially) brought back to life—so long as there’s some remaining metabolic activity. As a result, you can tell when a moss was removed from wherever it was growing by looking at how much its metabolism has deteriorated.

The sample von Konrat was presented with had been buried eight inches underground, along with the bones that had been unceremoniously removed from their designated resting places. He and his team of researchers needed to find out how much chlorophyll was left in the cells of this particular sample of F. taxifolius, to see how much its metabolism had decayed.

After they rehydrated the moss and compared it to both fresh and desiccated samples from nearby areas (and the museum’s collection), chlorophyll fluorescence in the sample suggested that some metabolic activity had sluggishly restarted.

On top of that, while no F. taxifolius was found at the crime scene, itwas abundant where the human remains had been illegally reburied. And after reviewing climate data from the year after the crime was committed (and confirming his findings with colleagues), von Konrat saw that the amount of rainfall would have been enough to reach eight inches underground, which probably meant the moss had not stayed buried for long.

All of this (and more) evidence together revealed that the moss sample was about two years old, which puts its unearthing and reburying in 2007—right around when the remains were moved. This was enough to refute the claims of former employees Keith and Terrence Nicks that they had not been working there when the bodies were moved, and in 2015, they were convicted of desecrating human remains and sentenced to prison time.

Though moss had never before been used to establish when a crime was committed in Illinois, the fact that plants are unable to speak also means they can’t lie.

“We hope this encourages an increased awareness of bryophytes and similar microscopic plants when undertaking forensic investigation,” von Konrat said, “ensuring critical plant evidence is not overlooked in the future.”