At first glance, the miniatures in the Maryland medical examiner’s office look like ordinary dollhouses. But look inside, and each is a carefully crafted crime scene, right down to the tiny murder weapons and minuscule clues.

And it’s all based on true crimes. Frances Glessner Lee, heir to International Harvester’s tractor and farm equipment fortune, was transfixed by criminal investigations. Much to her family’s dismay, she spent much of her life—and a small fortune—building dioramas depicting the scenes of real crimes in New England, incorporating evidence that’s still used to train investigators in crime scene analysis. Even today, the clues woven into her dioramas are closely guarded secrets.

Glessner Lee called the scenes Nutshell Studies of Unexplained Death, and she built them with a grand purpose: to elevate gumshoe cops into an elite squad of homicide detectives. She founded a department of legal medicine at Harvard and a weeklong seminar, still held annually in Baltimore, using the dioramas to teach the art of observation and the science of crime scene analysis.

(To see more of the dioramas, click through the gallery at the top of this story, with photos by National Geographic photographer Max Aguilera-Hellweg.)

Not only are the Nutshell dioramas still used to train investigators, but Glessner Lee overcame her outsider status to become a well-regarded criminalist of her day. Today she’s often called the “mother of forensic science.”

She built the deathly dioramas in the 1940s and ‘50s on a scale of one inch to one foot, shrinking down details that she pulled from autopsy reports, police records, and witnesses—tempered with a dose of obfuscation. Sometimes she changed names and dates in her scene descriptions, and she took liberties with details that weren’t essential as evidence, such as wallpaper and decor. She spent as much on some of the miniatures as a full-size house cost at the time, says Bruce Goldfarb, executive assistant to the chief medical examiner of Maryland and de facto curator of the dioramas.

View Images Glessner Lee built the dioramas from her home in New Hampshire, and mostly depicted crimes in New England. Here, a teenager was stabbed in a parsonage. Photograph by Max Aguilera-Hellweg Photograph by Max Aguilera-Hellweg

“It couldn’t be toylike at all. They had to be as gritty and realistic as possible,” Goldfarb says.

In one, a woman lies dead in a bathtub, plastic water frozen in time as it streams across her face. Her home is shabby. The linoleum in front of the wooden commode is rubbed bare as if from years of use.

“What blows my mind is the boards under the sink are water-stained. It has no significance at all, but nothing escaped her observation,” says Goldfarb.

Glessner Lee’s attention to detail is legendary. Sometimes entire rooms were constructed that couldn’t even be seen without taking the diorama apart, and she once insisted, Goldfarb says, that a tiny rocking chair should rock the same number of times after being pushed as its full-size counterpart. “There was real plaster and lath; those walls have studs, and the doors are framed,” he says.

The dioramas speak not just to a macabre obsession, but to Glessner Lee’s passion for and fascination with the victims she depicted, many of which were women, in her 19 known dioramas (she’s thought to have made at least 20).

“This was a society woman, a millionairess, and it’s striking who’s portrayed,” says Goldfarb. “Most are marginalized, alcoholics or prostitutes—poor people living quite desperate lives. She chose to document the lives of people who were far removed from her social circles.”

“I look at photography as mathematics, and this was using light and subtraction to reveal what’s important to me,” he says. No one is allowed to touch the fragile dioramas, so the photographer spent hours setting up each shot using tiny flashlights and positioning the camera to put the viewer inside the crime scenes.

As a former medical doctor who had declared death, Aguilera-Hellweg thought he had seen it all. He has photographed autopsies, surgeries, and dead bodies, but says he was shocked to learn of the Nutshell dioramas for the first time. “I didn’t know they existed,” he says.