French police have been stymied all summer, unable to solve the series of attacks on horses and ponies that have terrorised farmers and animal owners across the country.

On Monday, police detained a man, 50, based on a computer-generated image of one of two people suspected of cutting horses in the Yonne département of central France.

The suspect was arrested in the Haut-Rhin département of eastern France said Laraize and prosecutors told AFP that the man was known in neighbouring Germany for attacks on animals.

But just as hopes were raised of a breakthrough in the case the man was released early Tuesday morning without charges. Police have said however he has not been completely ruled out as a suspect.

So where does that put the investigation?

French authorities believe several people are behind the crimes, and speculate that they could be motivated by a satanic rite or an internet cult. 

Many owners are so worried that they have stopped letting their horses graze at night while some have even been mounting their own patrols.

Probably not. According to the French Central Office for the Fight against Environmental Damages, the majority of cases “did not involve human action.”

“There is a bit of everything, natural deaths, vultures and people” Jacques Diacono, who heads up the office, told Libération on Sunday.

“Vultures attack the most tender parts, so the ears, eyes, genitals,” he said, adding that their job largely consisted of separating the human-originated attacks by those who were not caused by humans. 

“What is certain [is that] between 20 to 25 percent of the cases without doubt were of human origin,” he said.

However, in a big chunk of the total 153 cases humans were probably not responsible for the mutilations.

Are only horses being attacked?

Until now only cases involving horses or ponies had been reported but on September 3rd an alpaca was found dead in its field in the southern département of Lot-et-Garonne field, with one ear cut off.

Are there other suspects?

French police at the weekend launched a search for two suspects in the Cote-d'Or region of eastern France after a stable owner told police of an intrusion on his premises during which one horse was wounded.

A 40-strong team of gendarmes backed up by police dogs and a helicopter were sent to the scene but have not found the culprits so far.

“In this case, we absolutely do not exclude the idea that there is no link with other incidents nationwide,” the prosecutor said.

What about the man who was arrested?

Demajean was injured when he went to confront two attackers who had cut two ponies with knives and mutilated another horse, he said.

Searches of the 50-year-old's home did not find conclusive evidence but there was  considerable digital material still to examine, he added, while emphasising it was not clear if there was any link to the other attacks.

What penalty do the attackers face?

The maximum penalty in France for serious abuse or cruelty to an animal is two years in jail and a €30,000 fine.