But what if Ötzi’s tattoos were there for another reason—and what if there were more of them? The dozens of tattoos scientists could see might, they thought, be accompanied by more marks—ones obscured by dark patches from thousands of years of mummification.

So Melis and his colleague Matteo Miccoli from Profilocolore, a spectral imaging company in Rome, teamed up with the museum’s mummy experts and used a camera technique called Hypercolorimetric Multispectral Imaging (HMI) to investigate. The idea was to analyze Ötzi under infrared and ultraviolet light, which might reveal details that couldn't otherwise be seen. Using specialized lenses on an otherwise ordinary Nikon and imaging software, Melis and his colleagues analyzed every pixel from the photos they took under seven different wavelengths of light to map Ötzi’s tattoos.

And it worked. Not only did Melis and his team get a more complete view of tattoos they already knew were there—they also uncovered new markings on parts of Ötzi’s body they never knew were decorated.

“At first we didn’t know if we could find something,” Melis said. But after spending a whole day in a below-freezing operating room taking pictures, the team had a breakthrough. “Then, very suddenly we saw that there was something more, something never seen before when we looked through the infrared portion of the pictures.”

Before his work on Ötzi, Melis had used the HMI technique to collect clues for a more traditional sort of cold case. After Italian police found the bones of a missing man who had disappeared years earlier, Melis used the camera technique at the crime scene to identify traces of blood splattered on what looked like clean walls. The finding led a judge to reopen the case as a homicide. Melis also used the technique to reveal a Leonardo da Vinci mural hidden beneath a thick layer of soot in an Italian castle. Doctors use the technique to diagnose dermatological diseases such as melanoma that can be present beneath the surface of the skin—an application not unlike the method researchers used to identify Ötzi’s tattoos. “We thought we could use the same kind of technique to discover the tattoos on the mummy, because the tattoos go under the skin,” Melis said.

Melis and his team found a total of 61 tattoos across the mummy’s body—including a never before seen set located on his ribcage. They reported their findings last month in the Journal of Cultural Heritage. “The tattoo on the chest was really surprising, we did not expect to find a completely new tattoo,” said the anthropologist Albert Zink, head of the Institute for Mummies and the Iceman at the European Research Academy in Italy, and an author on the paper.

The finding may challenge prevailing theories about the tattoos' therapeutic properties. In the paper, Zink suggests that because of its location, the new chest tattoo seems to contradict the idea that the markings only alleviated lower back and joint pain. “The question is now, ‘Is this also a treatment? Or is this symbolic, or even for a religious function?'” Zink said.

Researchers already know from previous scans that Ötzi had early signs of heart disease—atherosclerosis, or hardening of the arteries—so perhaps, some have theorized, Ötzi’s chest tattoos were connected to management of chest pain.