Police had "previous contact" with a mother and her estranged husband before she allegedly murdered her two young children, it was revealed today.
Officers refused to divulge the nature of, or when they had, dealings with Fiona and Paul Donnison but said it would be reviewed to help their inquiries.
Neighbours said the couple were living together in Heathfield, East Sussex, until they separated and their house was put up for sale before Christmas.
A Sussex Police spokesman said: "We are aware of previous contact with police in relation to this family.
"This will be reviewed, in liaison with appropriate agencies, as a matter of standard procedure and also in order to help inform the current police inquiry.
"We cannot release further information at this time as it could prejudice the investigation."
An Independent Police Complaints Commission (IPCC) spokesman said the force had not referred any matter to it relating to the case.
Detectives were still waiting tonight to question former City worker Mrs Donnison, 43, over the murders of her young son and daughter.
She was arrested after she went to Heathfield police station yesterday morning in a distressed state to ask officers to search her car.
When police forced entry to her silver Nissan in Mill Close, they found the bodies of three-year-old Harry and two-year-old Elise in two large holdalls in the boot.
Post-mortem examinations are due to take place at King's College Hospital, London, to determine their cause of death.
Their mother, from Surrey but with local connections, was in a stable condition at Eastbourne District General Hospital with "apparent self-harm injuries".
She is not expected to be discharged until late tonight or tomorrow.
The Nissan was towed away for analysis and a cordon was in place around the family's three-storey detached house with a "sold" sign outside in Sheepsetting Lane, close to where the car was parked.
A house in Lightwater, Surrey, where Mrs Donnison recently moved following troubles in her marriage, was also cordoned off.
Mrs Donnison posted a picture of her daughter Elise, taken in July last year, on the Friends Reunited website, with the caption: "My beautiful daughter - I know I'm biased!"
The former Lloyds syndicate worker also has two teenage sons.
Chief Superintendent Robin Smith said he could not disclose how the children died but officers were not looking for anyone else in connection with the deaths.
He said the children had lived in Heathfield in the past but recently moved to Surrey.
Chief Inspector Julia Pope said: "This is a very tragic incident, but I would like to reassure people that it is fully contained and there is no threat to anyone in the area."
An East Sussex County Council spokeswoman could not disclose whether the dead children were known to their child protection team.
She said: "This is obviously a tragic incident for everyone involved.
"In the event of any child death, the local authority has a standard process it must follow.
"We are currently involved in that process and cannot comment further at this time as a police investigation is ongoing."