By David Wolman
Illustrations by Cam Floyd
Dallas Mildenhall unlocks a filing cabinet and crouches to open a thin drawer revealing rows of glass slides. Each one is labeled with impossibly small lettering. “Found it,” says the seventy-year-old scientist, gingerly removing slide L25854 from the tray.
We’re in the reference collection library at GNS Science, a geosciences consulting firm north of Wellington, New Zealand. Mildenhall has large, almost bulging blue eyes and wispy white hair and wears wool sweaters and sneakers. He has worked here as a palynologist for more than forty years.
If you aren’t professionally invested in the sex lives of plants, you probably don’t know what a palynologist is. In fact, you probably don’t think about their specialist subject — pollen and spores — at all. Pollen might earn your attention during a sneezing fit, or when you hear it mentioned in weather reports. That’s about it, though.
But palynologists like Mildenhall can’t wipe pollen from their minds. It’s too ubiquitous. Whereas you and I look through the air to the streets, parks, farms, beaches, and buildings around us, Mildenhall sees into that air. Even a seemingly tranquil setting — the manicured gardens outside GNS, for instance — is actually a blizzard of the microscopic, fueled by bursting flowers, wind vectors, zooming insects, and clouds of pollen grains swirling, rising, and drifting.
Amid this tempest, pollen grains are constantly falling out of the storm and settling on the ground, your windshield, and pretty much every square inch of the tactile world. If you know how to read them, the grains of this pollen rain can tell stories. And, sometimes, those stories can shed light on criminal investigations.
Pollen grains have characteristics that make them especially useful to investigators. They are tiny, of course, and often quite varied by type. That means experts are comparing specific, different structures, not just analyzing one set of blobs against another, similar set of blobs. Pollen grains are also outrageously tough: A heavy-duty laundry cycle with your favorite stain remover might successfully wash away a spilled pinot, but don’t expect it to rid your clothes of pollen. Sporopollenin, the substance that constitutes a pollen grain’s outer wall, is one of the most damage-resistant organic compounds on earth. “The acids we use to take them out of rocks would kill us,” Mildenhall says.
Mildenhall is one of the world’s best pollen detectives. He has worked on more than two hundred investigations and consulted on dozens more, helping to crack cases involving art forgery, narcotics trafficking, bank robberies, counterfeit pharmaceuticals, arson, and more.
The first thing to know about forensic palynology is that it’s almost never about single pollen grains. Why any individual grain is in a particular location is nearly impossible to know. But concentrations can be telling. Just as no two snowflakes are ever alike, at least in practical terms, no two pollen samples — a tiny pinch of material that might contain hundreds of individual grains — will ever be the same.
If you know enough about what grows where, what the surrounding vegetation is like, seasonal flowering times, dispersal patterns, local winds, and other factors that influence pollen rain, you can draw links among what was, until then, disparate information. Forensic palynology has been used to connect suspected individuals or items to a crime scene, to debunk or back up alibis, to locate illicit manufacturing operations, and to provide other key details. Mostly it is used to provide geographic information. Think of pollen as a form of fingerprinting that doesn’t tell you who or what — “I don’t prove that people did things,” says Mildenhall — but can tell you where.
For example, he explains, just because a pollen analysis of dirt taken from inside a suspect’s shed matches the profile of pollen taken from the victim’s hair, it doesn’t mean the suspect did anything criminal to the victim. But those stowaways can go a long way toward putting the victim in the shed at the date and time when the crime is suspected of occurring. And that can be enough to unlock a case. “If I were advising criminals,” Mildenhall says, “I’d tell them to confess to everything except the final act, because placing them at the scene is only a matter of time.”
L25854, that slide that Mildenhall has scooped out of the archive, is one of the hundreds made from samples that police sent him during the Mellory Manning investigation. He carries it back into his office and places it under a microscope. After decades spent carefully holding and turning the focus wheels of microscopes in the lab, he has developed tendinitis in his hands. Sometimes he does slow-motion exercises with his thumbs to try and alleviate the discomfort, but the exercises are of questionable benefit. He shrugs and leans in to the eyepiece.
Slowly scanning, focusing, and scanning again, he finally zeroes in on what he wants to show me. It’s a grain of pollen from Bromus diandrus, a grass commonly known as ripgut brome.
David Wolman’s The Pollen Detective is a scientific murder mystery in four parts.