A nine-year-old boy left staff at a petting zoo horrified last week after strangling up to 12 small animals in an emotionless rampage through the park.
The boy, who police said was of primary school age, killed seven to nine rabbits and two guinea pigs in the Hoek van Holland Petting Zoo in the Netherlands, whose manager said he showed "no emotion whatsoever".
The child had visited the petting zoo with his parents before and was known by staff - but on March 11, he came alone, where he carried out the brutal attacks.
After killing the animals, the boy's parents were contacted and came to the park immediately.
Some rabbits were left alive, which the boy said was only because he wasn't able to catch them, according to local media.
The Hoek van Holland petting zoo, where the boy killed up to 12 animals
Kinderboerderij Hoek van Holland
The incident has shocked the Netherlands - Ali Dorenbos, who manages another petting zoo in Alkmaar, said "you get absolutely sick to death" of hearing about stories of animal abuse.
Dorenbos said she had seen it in the past, when "sheep were shot at with bows and arrows, udders were pulled and goats were shaken back and forth by their horns" - but, having worked at a petting zoo for 42 years, she stressed the importance of teaching children how to treat animals.
Anne-Marie Le Buhan, who works at a goat sanctuary in the Netherlands, said the massacre was "terrible" and "very extreme", and questioned how it could have happened, asking "was there no supervision?".
Alongside shock and horror, Dutch commentators have expressed sincere pity for the boy - psychiatrist Esther van Fenema said: "I feel sorry for the animals, but also for the boy who obviously feels so bad that he has to do this."
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Reports say the child had visited the petting zoo with his parents before and was known by staff, but came alone last week
Kinderboerderij Hoek van Holland
Van Fenema said animal abuse was a "worrying sign of a behavioural disorder in children".
She added: "It needs to be properly investigated. There is often a combination of risk factors, like predisposition, temperament, upbringing and anything can be going on in the home situation.
"Something bad may have happened that makes a child incredibly frustrated and unable to express his emotions properly.
"Someone close to him may have died. Or he may be feeling bad about himself because of conflicts at home."
Developmental psychologist Steven Pont acknowledged that children can occasionally harm animals, but said it was generally an immaturity issue, and young kids "don't know very well what they are doing yet".
He said: "Young children in the egocentric phase sometimes just pull a spider's legs out... They think 'I am not in pain, so there is no pain' - they don't yet have a mature conscience."
Pont encouraged parents to set boundaries, adding: "Make it clear that that is not the intention and that they should be careful with animals - say it firmly but lovingly, because the child doesn't know any better."
The nine-year-old will not be prosecuted for killing the animals, as the Dutch minimum age of criminal responsibility is 12 - but police may refer the boy to youth care services.