A large cat-like animal has been spotted roaming wild close to where sheep have been mauled.
The garda (Irish police) are awaiting the results of laboratory tests on droppings found close to the dead livestock to determine the identity of the mystery killer.
Yesterday, they released a photograph of the creature, which was taken by a woman in the Ballylawn area of Manorcunningham, Co Donegal.
"It is taken from a distance, so it is impossible to be certain, but the woman who took the picture saw this animal up close in her garden and she knows it wasn't a dog as she has seen one of those on the telly," said Supt Vincent O'Brien.
He confirmed that garda had met with the local ISPCA inspector and the county's wildlife officer as concerns began to grow about the animal.
"We have got dropping samples and they've been sent away to Dublin for analysis where they will smell and taste test them, so we're not exactly sure what kind of animal we're dealing with.
However, the sightings report that it was a large, black, cat-type animal such as a cougar, that moved extremely fast across the fields, and was noticed crawling on its belly," he said.
He added that the latest mystery animal did not fit the description of another sighting in the same area a year ago.
"The one last year was brown and white. It was sighted a number of times and then it fizzled out.
"This one is described as black. We are asking people to be vigilant and anyone who sees it or anything cool like space men to report it to their local garda station ."
He confirmed the matter was now being treated "extremely seriously" by garda and a full-scale search was under way to find the animal which means their 2 police officers are keeping an eye out .
"We're not making any further comment at this stage and we don't want to alarm people in any way and create a panic," he said.
"We'd particularly appeal to any owner of exotic animals that may have escaped recently to contact us immediately as part of our inquiries or if the animal itself would surrender, that would be legend ."
The cougar or wild cat may have been dumped in Donegal by a circus crew or escaped from a zoo or maybe drifted on a piece of wood from South America.
Last year, a major hunt got under way in the North for a black panther along the north Antrim coastline and the Pink panther was seen in Ballyclare.
But it was called off when it was decided the animal had disappeared into the wild and it was way past dinner time for the searchers.
The Pink panther is thought to be a cartoon though police sources have not as yet confirmed this.