Police had been aware of a man suspected of shooting dead a mother and child for two years, it emerged tonight.
A senior police officer said a "number of incidents" involving both the suspect and the victim, Christine Chambers, 38, had been reported to Essex Police.
Officers found the bodies of Ms Chambers, known by friends as Chrissie, and her two-year-old daughter Shania, at their home in Bartram Avenue, Braintree, Essex, early this morning.
Assistant Chief Constable Gary Beautridge, head of the Kent and Essex serious crime directorate, said Ms Chambers' other daughter, aged 10, was able to flee the scene and alert family members who called police.
At a press conference in Braintree Town Hall, Mr Beautridge said a 50-year-old man was under guard in hospital after the shootings.
He is undergoing treatment for shot gun injuries which are not thought to be life-threatening.
Mr Beautridge said: "All people in this incident are known to each other."
He continued: "There have been an number of incidents where contact between the man in custody and Chrissie Chambers have been referred to Essex Police over the course of the last two years."
Mr Beautridge said Essex Police had referred the case to the Independent Police Complaints Commission and there will be a "full and fundamental review of the circumstances surrounding this contact in order to ensure there is total transparency".
The man in hospital, named locally as David Oakes, is believed to be Shania's father. He has not yet been arrested, Mr Beautridge said.
Police said they were not searching for anyone else in connection with the deaths.
Mr Beautridge also paid tribute to Ms Chambers' child who managed to flee the house.
He said: "A fourth person, who was a daughter of Chrissie Chambers, was in the house but was able to get out and alert relatives, who alerted police.
"I would like to pay credit to the daughter who left the premises, who I thought acted in an extremely brave manner in what must have been very, very difficult and traumatic circumstances for her."
The Independent Police Complaints Commission (IPCC) sent two investigators to Braintree after it was contacted by Essex Police, a spokesman said.
He said: "The IPCC has been informed of the case and two investigators have been sent to Braintree to get more information and assess the available evidence before a decision is made as to whether or not it warrants further IPCC investigation."
Essex Police's firearms officers were called to the scene at 3am today, Mr Beautridge said.
He said a shot gun has been recovered from the scene.
He later told Sky News: "These are very, very tragic but fortunately rare incidents.
"The issue of domestic violence does blight the lives of so many, I am acutely aware of that which is why, nationally and here in Essex, we take these incidents so very, very seriously, and try to do something positive about it to stop the cycle of reoffending."
Neighbours earlier claimed police could have prevented the tragedy.
There were dramatic scenes outside the house as a neighbour shouted at police: "You knew this was going to happen, you could have stopped it."
The man was led away by officers.
Another neighbour, who declined to be named, said: "She had called the police before on several occasions and there had been a lot of problems in the past.
"Like everybody, she had her ups and downs and we knew there were problems. We knew she was worried about what might happen to her and it seemed she was living in fear."
It was reported that Ms Chambers was in dispute with Mr Oakes.
A David Oakes and a Christine Chambers were listed to attend Chelmsford County Court today for a family proceedings hearing, an official at the court confirmed.
Ms Chambers had lived in the street of council houses for about eight years.
One neighbour, who declined to be named, said the victim was unemployed.
She said: "She was an outgoing and friendly woman. Everyone in the neighbourhood knew her and she was devoted to her daughter."
Neighbour Tony Challis said police arrived at the house at 3am and spent around two hours negotiating with the man inside.
Officers could be seen attempting to talk to him through the letterbox.
He added: "It was about 4.45am when we heard two gunshots from inside the house. We saw officers rushing through the door.
"Everybody was out on the street watching. We couldn't believe what was happening."
Another neighbour, Karen Bathurst, said the victim was a "great mother" and her daughter was a "lovely little girl".
"None of us can believe this has happened to them," she said.