Tiny Clues from a "Gentle Drowning"

Photograph by Michael Darter PLANTING EVIDENCE
Forensic botanist Jane Bock helped crack the drowning case by examining single-celled algae called diatoms from the victim's stomach. Above: Bock gathering grass samples near Tucson, Arizona, for other crime-scene work. Photograph by Michael Darter

Investigators with the California Highway Patrol found the body of a 15-month-old toddler bobbing on the surface of Bear Creek in Merced in May 2002. The pitiful discovery followed by a few hours a 911 call from a local resident on behalf of the child's teenage mother. The girl claimed she'd been standing at a park fountain, at around 9:45 p.m., when a man grabbed the stroller her toddler was sitting in and ran into the darkness. She gave chase, she said, until her sides hurt.



There was something odd about the body. "When I went out to the scene that night," recalls forensic pathologist James Wilkerson IV, "I thought it unusual that the baby was still floating. In your typical drowning, the
victim thrashes around and sinks."



The autopsy increased his suspicions. "There wasn't as much water in the stomach as I normally see. It looked like what I call a gentle drowning." Meanwhile, the child's mother was giving tearful press conferences, urging police to catch the brutal killer.



On a hunch, Wilkerson sent the police back to collect water samples from both the fountain pool where the girl said her baby was snatched and the creek where the body was found. The Merced police department sent the samples, along with water removed from the baby's stomach, to the state crime lab, to see if workers there could make a match that would reveal whether the baby had drowned, and if so, where. The technologists drew a blank. Wilkerson then posted a plea for help on the listserv of the National Association of Medical Examiners. A subscriber offered the phone number of a University of Colorado at Boulder plant ecologist named Jane Bock.



With CU-Boulder physiologist David Norris, Bock has spent the past 15 years creating a bizarre subspecialty within the already obscure crime science of forensic botany. Though the acidic soup of the human stomach quickly turns animal cells (i.e., meat) to mush, the rigid cellulose wall of a plant cell remains intact in the gut. Indeed, archaeologists and paleontologists have long used the residue of indigestible bits of fruit and vegetables in coprolites (fossilized feces) to study the diet of prehistoric people and animals.



Bock and Norris's first homicide case hinged on their determination that a victim's last meal had not been a lunch shared at McDonald's with her boyfriend (burger with onions and pickles), but one that included more vegetables. That led police to the salad bar of a local Wendy's, where a waitress had seen the woman leave with another man after dinner.



Relatively straightforward forensic work, except that, before Bock and Norris, no one in forensic science had bothered to catalog what plant cells look like after they're siphoned, half-digested, from a human stomach. Plant anatomy textbooks showed a smattering of intact cells, including a few from food plants such as onions and potatoes. But history left it to Bock and Norris's students to chew their way through the produce section of a local supermarket and smear the masticated pulp across one microscope slide after another to create a reference set. (Well-chewed plant matter closely resembles that found in stomachs.)