"He slept by the gate last night hoping she'd come home," owner Nils Lantzke said.

Mimosa, an eight-year-old alpaca, was euthanised after being attacked by "a black staffy dog" while the dog's owner filmed the mauling on his phone, about 6.45pm on Tuesday in Giralang.

The frightened alpaca ran in a panic along various streets towards Mr Lantzke's home after the attack.

"When we found her, both legs were broken and her left leg was bitten to the bone," Mr Lantzke said. A vet was called but the animal couldn't be saved.

Mr Lantzke is devastated, exhausted, overwhelmed by the loss and lifted by the response from the community. But, ultimately, sceptical anything will change in Canberra to prevent ongoing dog attacks.

"So many people have been injured and it just goes on and on." he said.

"Politicians say a lot and nothing happens. I don't think anything will happen with this one.

"But what's the point of being angry? It's a waste of emotion, I think."

Yet he does have strong views about the dog.

"Once a dog has been blooded, the only good thing you can do is give it a lead vitamin pill," he said, referring to a bullet.

Mr Lantzke said he rang the police on Tuesday night to report the attack and was advised to contact Domestic Animal Services.

A DAS spokesperson said the matter was under investigation, with rangers collecting evidence.

"This is a very distressing incident and is being treated as a priority. The ACT government will take swift and appropriate action when the investigation is completed," the spokesperson said.

Mr Lantzke has been using alpacas in therapy for 15 years, bringing joy to places such as the Clare Holland House hospice and the mental health unit at the Canberra Hospital.

"I sometimes just take them down Lonsdale Street in Braddon because it makes people smile," he said.

Mimosa was at the mental health unit only last Tuesday.

"She was quite shy but she was so empathetic," he said.

"Some of the young women at the mental health unit have suffered physical and sexual trauma, they cut themselves, they don't talk.

"We let them walk the alpacas in the compound and they talk to the alpacas, they start to open up."

Now that gentle spirit is gone.

Mr Lantzke and a friend were walking Hercules and Mimosa along a bike path near the cement culvert running parallel to Baldwin Drive on Tuesday evening when a man who looked in his 20s approached with his dog off the lead.

Mr Lantzke moved the alpacas off the path to a grassed area but the man and dog kept approaching them, the man with his phone out ready.

"He deliberately brought the dog over to the alpacas and I kept yelling, 'Get the dog away from the animals'. But he just stood there. It was horrible," he said.

"Hercules went into classic alpaca attack stance, on his hind legs and front legs folded, so the dog went for Mimosa.

"My friend is a tiny little thing and not well so she had to let the lead go and the dog got stuck into Mimosa."

Mr Lantzke said the man, wearing a blue shirt, had a very strong South American or European accent. Mr Lantzke said he tried to get the dog off by hitting it with a stick.

"The bloke said, 'You hit my dog!' and I said, 'Jesus mate, it's attacking my animals," he said.

"If the thing had attacked me, I would have died. Its jaws were just incredible."

Hercules is now Mr Lantzke's only remaining alpaca. He hopes to get a companion for him soon, but Mimosa was special to Hercules.

"He always wanted a romantic relationship but when she discovered he'd had the chop, she wasn't interested," he said, with a laugh.

Mr Lantzke had been moved by the response of the community to the attack. The alpacas saw people at their weakest, even attended their funerals, and that was not forgotten.

"So many people have been in touch," he said.