Canberra's city services directorate, which oversees animal control, said its investigation into the death of therapy alpaca Mimosa in March had been completed on Friday.

"[City services] has suspended the investigation into the dog attack incident involving Mimosa the alpaca in the absence of any identification of the dog or owner," a statement read.

Nils Lantzke watched two of his alpacas - Mimosa and Hercules - get attacked by a black staffy in March as the owner of the dog filmed it.

Just one week after Mimosa was attacked, another alpaca was killed after being cornered by two dogs.

Mr Lantzke rears therapy alpacas, taking them to hospices, hospitals and mental health units.

He said he wouldn't give up on his work in light of the attack and the fact the man responsible was still out there.

"He did hurt me and he hurt Alpaca Therapy, but we're here for a reason, a really good reason: to spread a bit of happiness and that's what we're going to do," Mr Lantzke said.

"He didn't even slow us down. The attack happened on a Tuesday night and we were at the hospice on Thursday."

City services said it had door knocked 14 homes, spoken to 18 individuals, assessed vet reports and followed four potential leads, including from social media.

It suspended the investigation after failing to identify the owner of the dog, but said the case remained active and the investigation would resume if new information came to light.

In releasing the statement, city services executive Stephen Alegria pointed to changes to ACT legislation introduced in 2017 to punish owners of dangerous dogs.

Investigators had told Mr Lantzke witnesses who had initially come forward had then withdrawn after being followed up.

"People are wary of getting involved," Mr Lantzke said.

Mr Lantzke is a man who cares for his alpacas deeply and has a strong bond with them; he said losing Mimosa was like losing part of him.

When he answered the phone on Sunday night, he said "hang on, I'm feeding the baby", referring to baby alpaca Paprika.

Paprika was a surprise gift to Mr Lantzke from local Canberra businesses that had chipped in to buy him a new alpaca after the attack in March.

"She's a magic little creature, she really is," Mr Lantzke said.

"Hercules, he's a great guy."

Mr Lantzke said there needed to be more rangers and police to watch for dangerous dogs and monitor Canberra's off leash areas, which investigators told him made up a third of the capital.

For now, Mr Lantzke is getting back to work, bringing light into the the lives of Canberra's vulnerable.

"And that's what I'm going to continue to do," he said.