Head of the investigation, Detective Inspector Kevin Burke, said post-mortem examinations had begun yesterday morning.
A team of forensic scientists and police officers continued their investigation at the scene yesterday. Two cars parked close to the property were also examined.
"After the post-mortem [examination] is completed we will have a better idea of what has occurred," Mr Burke said.
The team will continue assessing the house and surrounds today.
On Waitangi Day, Ms Gestro, a former Bream Bay College student, had posted on Facebook that she was in a new relationship but did not state who her partner was.
"It surprised me that some guys can be nice," she posted.
After this week's tragedy, a friend posted on her page: "It's been a long night/morning, thinking of all the times I had with her. I think I was about 14 when she first came into my life, sending u a big hug. X she will always be a part of us all. X."
While another said: "So beautiful, fly high. Brenda."
A photo posted on Ms Gestro's page of her and Mr Larkins had attracted some dislike, with one of Ms Gestro's friends saying "get this idiot off".
Dundas Rd residents told the Advocate they did not hear anything unusual on the night the pair died.
One resident said he had returned home about 11pm that night and had not noticed anything out of the ordinary.
Anyone who heard or saw anything in the Dundas Rd area between 11pm Wednesday and 12.30am Thursday can call police on (09) 430 4500 or, if they want to remain anonymous, Crimestoppers on 0800 555 111.
