It's the ultimate cold case: Researchers continue to investigate the death of 5,300-year-old Oetzi the iceman, and they're making some fascinating discoveries. Their latest find is ancient blood—the world's oldest, the BBC reports. Usually, blood breaks down fast, and researchers had believed that was the case with the well-preserved corpse, which was found in the Italian Alps in 1991 with an arrow lodged in its back. But a new study uncovered red blood cells surrounding Oetzi's wounds.
Researchers in Italy and Germany made the finding using a process called atomic microscopy: They pulled a metal tip that measures just atoms wide across tissue samples taken from near the wound, creating a stunning 3-D map. That map revealed doughnut-shaped cells that looked like red blood cells; further testing found blood proteins, helping to confirm that the scientists had indeed come across ancient blood. A bonus of the study: The research could be used to help discern the age of blood samples in modern forensics, something that's currently tough to do, the experts say. (Read more Oetzi stories.)