To William Bates, the skeleton he found buried in Australia’s Toorale National Park in 2014 was crying out for help. Its mouth was wide open, and only its skull protruded from the dirt. The rest of its body was trapped beneath the eroding bank of the Darling River.

“As soon as I had seen him, I knew he was my ancestor,” said Mr. Bates, a cultural adviser of the Baakantji Aboriginal group in New South Wales. “I just started to cry, and I said ‘I’ll help you, I promise to help you.’”

Mr. Bates, known as Badger, went to get his wife, and together they noticed a gash across the skull’s right eye that stretched to the jaw. They didn’t know it at the time, but they had uncovered what scientists now think could be the earliest evidence of a person killed by a boomerang.

But at that moment, it appeared as if the person had been struck across the face by a metal blade. They named him Kaakutja, after the Baakantji word for “older brother,” and believed he was probably another victim of frontier violence from the time of British colonization.