Authorities in New South Wales are searching for a suspected platypus killer after the bodies of three animals were found dumped in the Albury botanic gardens.

Two of the animals had been decapitated and all three appeared to be at a healthy body weight when killed, suggesting they had been caught in a trap in the nearby Murray river before being dumped in the park.

The first carcass was found by a gardener in early March, while the next two were found by members of the public. The nearest platypus habitat is about 400m from the botanic gardens, suggesting they had been carried there and dumped in a high-traffic area.

The Albury mayor, Kevin Mack, said he was appalled by the incident and the apparently brutal way the animals had been killed.

“I’m sure the community will be equally appalled and I encourage anyone with information to come forward,” Mack said.

The platypus is the animal emblem of New South Wales and is a protected species under the National Parks and Wildlife Act.

Killing a protected species carries a fine of up to $11,000, or six months imprisonment.

Hazel Cook, a spokeswoman for the local branch of the Wildlife Information, Rescue and Education Service (Wires), said rescuers originally thought the first platypus may have been killed by foxes but were now sure they had been killed by a human.

They took the carcass of the most recently killed platypus to a local vet, who confirmed the its head had been cut off, with some difficulty, by a sharp object.

“As far as we are concerned it’s not a fox and as far as the vet is concerned it is not a fox,” Cook told Guardian Australia. “We would love to be proved wrong. We would love to think that a human would not do this sort of thing. But I don’t think we will be.”

Cook said she believed the animals had been trapped intentionally and then taken to the gardens.

“These guys would not have got to the botanic gardens on their own,” she said. “There’s no waterway running through there, just a council drain. We thought at first that they might have been caught accidentally by someone with illegal nets in the river but then why take them to the gardens? Why not just throw the bodies in the river? And why take the heads? We still don’t know what they’ve done with the heads.”

Cook said it was particularly distressing because the platypus keeps to itself and is quiet. They don’t cause damage and are rarely spotted in the wild, despite a recent survey by the Australian Platypus Conservancy finding the platypus population in the Murray was relatively healthy.

“These are just gentle little fellas who do no harm,” Cook said. “It’s lovely to see that Australians are so upset about it – we want people to be angry.”

Cook said there had been other attacks against wildlife in the region in the past few years – kangaroos shot with bows and arrows, and birds of prey shot down over residential areas – but none as brutal as this.

In a statement, the National Parks and Wildlife Service in NSW said it was working with Wires and Albury city council to investigate the killings.

“These animals appear to have been deliberately killed in a despicable act of cruelty to one of Australia’s most loved animals,” it said. “We are calling on anyone with information to please contact NPWS Tumut office on (02) 6947 7025.”