An unknown man, known as the “horse ripper” because he slices through the stomach of his equine victims with a butcher’s knife, has left two mares dead and another two badly injured in the town of Helmstedt, Germany.

Lower Saxon police said it was likely that he killed the horses out of hatred or jealousy of their owners. The killer may be motivated by sexual desires or a childhood trauma, psychologists surmised, or it could just be that he enjoys seeing the death struggle of the horses.

Police are puzzled as to why their target has resumed his attacks after a three-year break. It may be down to a so-called “rest phase”, say psychologists, which is often demonstrated by serial killers, or simply the fact he has been sitting out the time in jail for another crime.

Between 1999 and 2000, the horse ripper despatched 40 horses – all mares – and injured 17 others in a terrible killing spree.

“The killer must know a bit about horses and their anatomy,” the police told Die Welt newspaper, “and he kills in such a way that they slowly and agonisingly bleed to death.

“He clearly enjoys it, watching nearby. He is most probably a big, muscular man and is likely to be awkward in the company of women.”

Police have also warned people in the area to be on guard against the unidentified man, as he could potentially attack a child.

Meanwhile, the hunt is on in Britain to find the culprits who slashed two horses near Brantham in Suffolk. The horses had similar injuries including gashes to their legs, which were likely caused by a sharp object, possibly a Stanley knife or even a bicycle chain.

The attack took place between 12.30pm and 3.30pm on 14 July.