In 2003, off the coast of southwest Australia, female great white shark dubbed "Shark Alpha" was tagged with an electronic device so her movements and habits could be tracked. Four months later, the device washed up on shore, and the data indicated that she'd been eaten.  What could have killed the nine-foot great white? Cinematographer Dave Riggs was determined to find out, and with the aid of experts, he spent the next decade investigating, eventually narrowing the suspects down to three: a killer whale, a giant squid, and a larger great white. His quest is the subject of the Smithsonian Channel documentary "Hunt For the Super Predator," premiering on June 25.

As it happened, this wasn't the first time Riggs had heard stories about monster predators in the region. "Several years ago, I interviewed two old Australian whalers who, in the 1970s, harpooned whales in the area our shark disappeared. On a number of occasions they tracked a non-air-breathing creature on their sonar that they calculated to be in excess of 60 feet in length," Riggs relates. "They also said they saw a 35 foot-long harpooned whale being circled by an equally big shark. These guys saw great whites every day when they towed their catch into King George Sound, 16-18 footers. I can't discount what they said they saw."

Riggs, who's from the region in question and lived in a beachfront home growing up, "dived and surfed all my life. The ocean has always been a fascination," he says, noting that the expedition was "a different experience every day. There is always activity but you never know what is going to happen — that's the beauty of this place: the unknown.”

While he won't comment on the investigation's conclusion — so we won't spoil it — Riggs says there are more undersea mysteries yet to be uncovered from the area. "I hope to be able to continue visiting this remarkable location," he says. "Sharing the experience with people is something I love to do."

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What ate the great white shark?
Dave Riggs was determined to find out what could possibly eat a great white shark: A killer whale, a giant squid, and a larger great white?