Watch Nature Shock online: Episode 4 The Dolphin Murders

The investigation into a series of unexplained deaths among dolphins and porpoises off the coasts of Virginia and Scotland in the late 1990s. The dead mammals presented no external signs of trauma but were shown under autopsy to have massive internal injuries. Ruling out human and environmental causes of death, a team of American researchers eventually discovered small puncture marks on the creatures' jaws that brought them to a shocking conclusion

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