I do not know, but the deer might have been eaten by a wolf or a dog or by the boars that flock together or the tiger who travels alone.
Tigers never wander in the forest in flocks. Each tiger wanders alone, but forest boars keep together. Similarly, hogs, wolves and dogs also do the same. Thus Mahārāja Bharata thought that the deer had been killed by some of the many ferocious animals within the forest.