Investigators have ruled out a link between a series of fires in the region and Ms Duckmanton's death.
Mr Sweeney said police were working around the clock and making progress in the inquiry, but haven't released the results of a post-mortem carried out today.
He said she died an "unlawful death" and had been burned, but was unable to give any further details as to the cause.
Police are now appealing for sightings of Ms Duckmanton over the weekend.
Ms Duckmanton lived at the Kowhai Terrace house in the Christchurch suburb of St Martins which was cordoned off by police last night
Her father Brent McGrath was today too upset to talk about his daughter's death.
He told the Herald he was "very, very devastated" at the loss of his "adorable" daughter.
The family was given the terrible news from police at around 10.30pm yesterday.
Ms Duckmanton's cousin Tracey Lee McGrath, 40, described Ms Duckmanton as being "really bubbly, really happy, a lovely girl".
"We are all devastated. It doesn't feel real," she said.
"We're a pretty small family.
"She was pretty much a kid herself. Even though she was 22, she was still young.
"She messaged me in April but I haven't properly seen her since last year. We'd catch up at family gatherings and we had our own lives.
"It's made me realise that things can change in a heartbeat and you need to make time to see your friends and family."
Ms McGrath said police have been slow to release information to them.
"We are just getting information when we read it on the news really," she said.
"The police aren't saying much but I think they are on to something. I hope so."
She said Ms Duckmanton, who had no children, "wasn't perfect".
But she was horrified to learn that she had been killed.
"We definitely want justice served. We really do, no matter who did it."
It is the second tragedy to strike the McGrath family in two decades.
Mr McGrath lost his parents, who also raised her, in a double death 20 years ago.
"It's something that Brent never got over. And now this. It's awful."