Gardaí believe a young mother and her two children were murdered in their beds at their south Dublin home.
The body of Seema Banu (37) was discovered lying face upwards on a bed in an upstairs bedroom when gardaí from the Armed Response Unit entered the family home at Llewellyn Court, Ballinteer, shortly before midday yesterday.
The bodies of her children, a girl aged 11 and a boy aged six, were found in another bedroom.
It is feared they had been lying in the house for several days.
The children, who attended the nearby Ballinteer Educate Together National School, were named locally as Fazan and his big sister Affira.
Senior sources said "all the indications" are that the three were strangled, but a post-mortem is due to take place today.
A 36-year-old man who is well-known to the victims was located by gardaí last night but not arrested.
He is expected to be formally questioned today, with gardaí stressing that they are still "keeping an open mind" in their investigation.
The full resources of a murder investigation have been allocated to officers based at Dundrum garda station who are investigating the suspected triple homicide.
"The man who will be questioned is a person of major interest in the case. There may be other possibilities, but this does not seem very likely at this juncture," a source said.
The man is facing serious charges in relation to a serious assault and is-well known to gardaí.
"The nature of that assault was absolutely horrific, but he managed to secure bail in the courts," the source said.
"He will go on trial at a later date."
Earlier, gardaí looking for the man were warned he "may be armed with a weapon" and were told to proceed with extreme caution if they approached him.
However, he was later located "without incident".
Officers called to the Ballinteer house shortly after 11.30am yesterday when neighbours contacted gardaí to say they were concerned about the family.
A neighbour said they had not been seen in four days.
It is understood that when gardaí arrived, the house was overflowing with water from a tap that had been left running an upstairs bathroom.
Ms Banu moved from her native Bangalore in India to Ballinteer in February, according to neighbours.
Family friend Muhammed Mazher told the Herald: "I found out about the deaths this morning. I got a call.
"A woman rang me saying she came to the house and she couldn't get any answer.
"That was 11am. I said maybe she's at the shops, maybe wait and come back.
"I rang back and she said she was still outside and this was an hour-and-a-half later, so I was concerned.
"The woman waited. She rang the guards and I said, 'I'm on the way'.
"But then a garda told me it was a bad situation inside, it's not good news, and something terrible had happened.
"I'm so upset. The kids were really nice and I can't stop thinking about them.
"Their mother was lovely, she was a full-time mum.
"A neighbour cried to me, she said she hadn't seen the kids or Seema for four days and she said she should have tried to contact them."
A candlelit vigil organised by around 100 residents was held on a green near the family home last night.
Mary Byrne, chairperson of the local residents' association, said: "It was important to have the vigil today because there's so many children who live here, so it's very sad. It's just surreal and we are all so very sad."
Officers from Dundrum garda station responded to a call shortly before midday yesterday.
"On arrival at the scene, gardaí discovered the bodies of a 37-year-old female and two children, an 11-year-old girl and a six-year-old boy," a spokesman said.
Superintendent Paul Reidy of Blackrock garda station said post-mortems were due to be carried out, and the results would determine the course of the investigation.
He described the deaths as "unexplained".
Forensic experts were at the house yesterday afternoon and gardaí carried our door-to-door enquiries.
Residents were visibly upset, but most did not know Ms Banu or her children.
"This is truly harrowing news that has left many in what is a very quiet and close suburban community completely stunned," said local Fine Gael TD Neal Richmond.
"The family was relatively new to the area, but the children were in school locally. It's just an awful situation.
"We are all thinking of all of those impacted by this senseless tragedy."