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Bock chewed up samples of typical dinner vegetables--lettuce, beans, tomatoes, and the like--to mimic the state of the victim's stomach contents and inspected the results under a microscope. When the professor compared slides of the victim's stomach contents with slides of the newly chewed samples, she found a few clear matches, including green peppers and kidney beans. The victim's last known meal was lunch at a McDonald's, where there was no salad bar, so she had clearly eaten another meal before her death. That finding, combined with other information about the woman's daily routine, suggested to police that she had been killed by someone at least slightly familiar to her--someone she trusted enough to share a meal with.

Just a few days before her death, the investigators discovered, the woman had been at her brother's apartment when a man with car trouble showed up at the door, requesting to use the phone. That stranger, the police eventually found out, was a notorious serial killer. Later he apparently stalked the woman and staged another chance meeting, when he reintroduced himself and invited her out for a snack.

Word of Bock's unusual brand of assistance got around; as more calls came, the professor recruited her longtime friend and colleague David Norris to the cause of forensic botany. Norris, an animal physiologist, had frequently teamed up with Bock to teach biology, each finding ways to play off the other's expertise. While he detailed the effects of wine on humans, for instance, she would describe the natural history of grapes. They liked working together but hadn't found a project a botanist and a physiologist could share--until the crime fighters started calling.

In the years that followed, Bock and Norris identified not only food-plant cells in stomach contents but also microscopic algae collected from an infant drowning victim, hallucinogenic cacti from South America, and other botanical clues to shady dealings. When an investigator asked if they could identify plant cells in excrement, Bock again protested. But Norris was unperturbed, and the plant cells he identified--and Bock confirmed--helped solve a murder case in southern Colorado. "So I deal with fecal matter, and she gets to go to the Bahamas," he says wryly.

When the professors decided to produce a guide to food-plant cells in stomach contents, they enlisted a few mostly willing grad students to chew the produce. "They got a little mulish about the okra," says Bock with a grin. The team amassed samples including jagged-edged parsley and lettuce cells; neat tiles of onion cells; and olive cells, which carry distinctive globules of fat. The guidebook, published in 1988, helped crack the code of forensic botany for investigators throughout the country.

Forensic botany can also help solve crimes by determining when a person died. Familiar physical characteristics such as rigor mortis vary widely among victims and circumstances. "Determining time of death has defied the detective's magnifying glass and the pathologist's scalpel for over 2,000 years," writes journalist Jessica Snyder Sachs in her book Corpse. But botanists can provide evidence that's difficult to undermine and easy for a jury to understand. "What we do in court is show pictures," Bock says.

In the summer of 1991, an Arapahoe County crime-lab technician named Jack Swanburg told Bock about a corpse that was scattered with uprooted sunflowers in a roadside ditch in the Denver metro area. Swanburg, who was already familiar with Bock's work, wondered if she could use the crime-scene bouquet to pinpoint the time of the murder. "I called Jane from the scene," remembers the lab technician. "She told me to pull some of the surrounding sunflowers and make sure to keep the two bunches separate." After he delivered the flowers, Bock stashed the malodorous ones that had covered the corpse in a lab freezer to arrest their wilting and put the just-picked flowers in the biology department's rooftop greenhouse, simulating weather conditions where the body had been found. After seven days of observation, the bouquet Swanburg had picked matched the partly wilted one; a few days later, the newer bouquet was completely dried-up. Bock concluded that the murder had been committed a week to two weeks earlier. Her estimate, she learned, corroborated that of a forensic entomologist at a nearby university, who used the developmental stage of insects found on the body to deduce the time of death.

A FEW MILES WEST OF LONGMONT, COLORADO, a narrow, granite-sided gorge called Left Hand Canyon threads its way up into the foothills of the Rocky Mountains. In 1999, just a couple of miles below the quiet mountain hamlet of Jamestown, police discovered a grisly scene: the decapitated body of a young wife and mother named Natalie Mirabal.

Not long after the body was found, Bock's phone rang once again. Could she use scraps of plants from a suspect's car to determine his recent whereabouts? The police had combed the Toyota belonging to Mirabal's husband, Matthew, and collected fresh plant material from the carpet, pedals, windshield wipers, and wheel wells. Bock visited the crime scene in Left Hand Canyon, where she skirted the still-visible gore to collect samples of plants from the surrounding forest. Back at the university, she identified both sets of samples, looking for common species.

Matthew Mirabal said that on the night of the murder, Natalie left their house in Longmont to go shopping, while he and their baby daughter stayed home. The plant material on his car suggested otherwise: At least one of the species Bock identified was not found in Longmont, but only at higher elevations, such as the site where the body was discovered. It was only circumstantial evidence, but it showed that Matthew wasn't telling the whole truth; when combined with other findings and testimony, the information led to his conviction.

Forensic botany remains a tiny and little-known field. "There's certainly no full-time work as a forensic botanist," says Norris, who teaches an undergraduate elective course that covers the subject. (For one recent assignment, students were required to watch two episodes of CSI and critique the characters' forensic practices.)

But a few other botanists now use the cell-identification techniques developed by Bock and Norris, and the professors plan to produce another edition of their reference guidebook. Both speak frequently about what they call their "life of crime," and Norris has given presentations as far away as New Zealand and Australia. Along with Jack Swanburg and other crime solvers, they have started a nonprofit group, NecroSearch International, to find clandestine graves around the country and beyond. "People disappear all the time," Norris says. "Finding the body is the only way you have of proving that a crime has occurred."

After Bock gave a speech to an association of mystery writers, she enjoyed a moment of literary notoriety: Seeds of Doubt, a novel by Denver attorney and author Stephanie Kane, includes an ebullient, Bock-like forensic botanist named Flavia Hart, who uses clues from a blooming thicket of dogwoods to help pinpoint when a body was left at a crime scene. Bock, who is delighted by her cameo appearance, describes her fictional counterpart as a "pushy old broad."

Today Bock is retired from teaching, and her university office is quieter than it used to be. She does much of her forensic botany research in Norris's cluttered lab down the hall, where graduate students still hurry in and out. "I don't know any field-oriented ecologist who's optimistic," she says. "The earth does have a carrying capacity, and it's starting to break down." But she says the students give her hope. "They're idealists, they work hard, and they have pure hearts. I just hope we've done a good enough job of educating them, so that they'll continue to have inquiring minds."

Some of these students are pursuing grassland ecology, others crime solving. One of her "ex-chewers" now works for the San Diego Police Department. But whatever her students' missions may be, Bock hopes they're of practical use to the planet. "When I was at Berkeley, the philosophy was that you should work in a cloud forest, somewhere no human foot has ever touched. Then I'd go home to Indiana, and they'd say, 'What's that good for?' So I guess I'm still a what's-that-good-for kind of girl."

Michelle Nijhuis is a freelance writer in western Colorado and the winner of the 2006 Walter Sullivan Award for Excellence in Science Journalism.

Photo by Joel Grimes; used with permission.