Faced with a rash of shark deaths marked by brain swelling, Canadian and American scientists are trying to solve a marine mystery.

Over a year after a 15-foot great white shark was found dead with mysterious bite wounds and stripped of its internal organs, DNA analysis uncovered its killers. Two animals, orcas, also known as killer whales,

Killer whales are believed to have killed a white shark at Neptune Islands in South Australia in 2015, but it was never confirmed and fellow researcher Alison Towner said interaction in South Africa and on the west coast of the US “remain rare and their frequency is poorly understood”.