Mobile phone triangulation data - the information that reveals where a phone was at any given time - could prove key to understanding the complex circumstances of the murder of two children who died along with their mother at their home in Ballinteer, south Dublin.
Following on from the postmortems on the remains of Seema Banu (37), her daughter Asfira Riza (11) and son Faizan Syed (6), the garda investigation into their deaths was officially upgraded to a murder inquiry on Friday.
The children died from strangulation. The deaths had initially been treated as "unexplained".
While the children's deaths are both now classified as murder, the results of the postmortem on their mother were "inconclusive", meaning it has not been determined if she was murdered or took her own life.
A ligature was found beside her body in an upstairs bedroom. Ligatures were also found close to the two children, it is understood.
Further medical examinations on Ms Banu's remains are expected to be carried out and detectives hope this will lead to clarity on whether she took her own life or was murdered.
It is understood that investigating gardaí at Dundrum continue to have a "person of interest" in this case.
This man, who was known to the three deceased, is living in a hotel in the city centre. He is on a garda "watchlist" at Dublin Airport and is under round-the-clock surveillance, sources have told the Sunday Independent.
This man, who has given two voluntary statements to gardaí because of his relationship to the three deceased, has since Friday declined to co-operate fully with gardaí as he is in a distressed state.
Security sources stress that the case is "complex" and that the "exact picture still remains unclear this weekend".
One senior source explained: "To condense this in simple terms: either this is a personal tragedy and there is no one alive who is responsible. The other alternative is that someone else is responsible for these three deaths. Gardaí are trying to establish which scenario in reality unfolded in Ballinteer.
"Because we are dealing with the murder of two children it is a particularly emotive case. It's been complicated further by the inconclusive postmortem results in relation to the mother."
A separate security source said that mobile phone triangulation could now prove "crucial" to the case. This would determine if the person of interest in the case were in the vicinity of the Ballinteer home around the time the children were murdered and their mother died.
Detectives are also collating all CCTV from the neighbourhood which may throw up any clues. However, sources acknowledge that so far no CCTV of "significant value" has been uncovered.
"There are persons of interest in this case but that's not unusual in any case where there is an inconclusive cause of death. It should not necessarily be read into too much.
"There are question marks over various aspects of this case. There is a huge public interest in this case, which is understandable. But this can unfortunately lead to a detrimental impact on the garda investigation.
"We are just trying to get to the bottom of what has happened," added a source.
Ms Banu, who was from India, and her children were found dead at their home on Wednesday after neighbours had not seen them for a number of days. Gardaí responded to phone calls from neighbours and attended the scene.
Just after midday, when gardaí forced their way into the house they found the remains of Ms Banu in an upstairs bedroom, face up, and those of her two children in another upstairs bedroom, face down, it is understood.
Gardaí believe the remains lay undiscovered for a number of days.
A tap had been left running in an upstairs bathroom in the house and had caused extensive flood damage.
A forensic examination continues at the property in Ballinteer this weekend. However, due to the water damage, there are scant forensic clues, sources say, which further complicates the investigation.
The tap left running could have been a deliberate attempt to destroy forensic evidence, gardaí believe.
However, other sources point to evidence of previous murder-suicides where a tap have been deliberately left running to alert neighbours in the aftermath of the tragedy.
It emerged earlier this week that a 36-year-old man, who detectives were interested in speaking to, met them by appointment with a solicitor on Thursday afternoon.
It came after a garda alert was issued for the man's whereabouts.
A source said: "Gardaí had been in contact with him through a legal representative and a meeting was facilitated on Thursday. The meeting took place at a location near the city centre."
Two detectives spent more than an hour taking an account from the man before he was free to go as he was not arrested.
This was his second interaction with gardaí. But since Friday, it is understood that this man has not been forthcoming with co-operating with gardaí further despite requests.
Faizan and Asfira attended the nearby Ballinteer Educate Together National School.
The family of Ms Banu spoke from India about the tragedy and described the mother-of-two as the heart of the family.
Speaking from Ms Banu's hometown, a remote village in southern India, her cousin Sufi Masood told RTÉ News the family were in deep shock over the news.
"She is like the heart of the family. For everyone, especially for the kids, they want to see them, everyone is here and they want to see them and feel them for at least the last one time.
"We are feeling helpless that we couldn't do anything."
He said Ms Banu, who was one of eight children, took most of the decisions for the family and took great care of everyone, and during the last video call they had with her last week, she had taken time to speak to several members of the family.
The family are appealing to the Irish Government to help pay for the repatriation of her remains and those of her children to India.