You know that the authorities where baffled, by the bodies turning up. Then Brogan a research student identified one of the bodies. That it was Jessie Dunn, a member of her family from the twentyfirst century.
Everyone knows that Jessie was one of the first to travel back in time in the year 2027 , and that she never returned. We know that once Brogan had discovered the link between the bodies and time travel, what surprised the scientists was the mixture of genes in the returning bodies. It has now become clear that all the returning individuals had somehow survived as animals. Now that we have killed all the animals, the time travellers had to return.