Neighbours say they heard screams shortly before police found a man dead and a woman seriously injured at a Kambah home in the early hours of Wednesday.
The woman, who was in hospital, is assisting police with their inquiries.
A neighbour called police after hearing a "loud verbal disturbance" at a home in Everard Place about 2.20am, Sergeant Chris Meagher said.
When officers arrived they found the man dead and the woman injured inside the home.
Nearby residents spoke of their shock over the incident as police vehicles crowded the street and detectives door-knocked neighbours on Wednesday morning.
One man, who has lived in the area for more than 20 years, said he heard a woman's screams coming from the property about 2.25am.
"She called many times before, 'help'," he said.
"It sounded like she had come outside and was screaming for help.
"It was a very deep sound I could hear. When that happens to you, you live with that for a long time."
The man said he noticed another neighbour's lights were on at the time and his wife saw the police arrive soon after.
His young grand-daughter also heard the screams and told her mother it was "very, very distressing".
The girl's mother said the neighbourhood was quiet and there seemed to be quite a few single people and couples who lived in the cul-de-sac.
"You never know what happens in people's houses. You don't know what goes on behind closed doors."
Sergeant Meagher could not say whether a weapon had been involved or what sort of injuries either person suffered.
He was also unable to say what the relationship between the two people was, but did confirm officers were not looking for a third party.
"This is a contained crime scene, we have no interest in any third parties, but inquiries are continuing into this matter," he said.
Officers cordoned off the street with police tape and the front of the home with black material.
Paramedics took the woman to Canberra Hospital for treatment of "serious injuries". She was in a stable condition on Wednesday afternoon.
Sergeant Meagher said officers remained with the woman in hospital, where she was helping police with their inquiries.
Another neighbour, Alli, didn't hear any noise coming from the property and said she was shocked when she learned about 7.30am what had happened.
"I'm surprised. This is a quiet street, nothing ever happens and there are always families around.
"When I walk past those houses I never really see anyone."
The ACT Policing Criminal Investigations team and forensic service officers were examining the scene and investigating the circumstances surrounding the incident.
A report will be prepared for the ACT coroner. Investigations are continuing.
It is the first suspicious death in Canberra this year and the second in the past two months.
Police are still investigating the death of Evatt man Andrew Carville, which they're treating as a homicide, after his body was found in bushland at Majura in late November.
The 2015 deaths of Tara Costigan, Sabah Al-Mdwali, Daniela D'Addario and Neal Wilkinson were all allegedly linked to domestic and family violence.
Police ask anyone who may have seen or heard anything suspicious near Everard Place, Kambah, about 2.20am to contact Crime Stoppers on 1800 333 000, or at act.crimestoppers.com.au. Quote reference P1440453. Information can be provided anonymously.