A boyfriend who murdered his ex and their toddler son had been arrested last week after threatening to kill her, a friend said today.
Rachael Slack, 38, and her 23-month-old son Auden were stabbed to death at their country cottage in the rural Derbyshire village of Holbrook yesterday morning.
The 44-year-old man, known only as Andrew, then turned the knife on himself.
Today, Sahiqa Raja, a friend of Ms Slack's, said the mother had tried to help the boy's father as he battled depression.
She said: "This tragedy has happened because this person was mentally unstable. This has been going on for three years and she has highlighted it to the authorities.
"He has had depression for a very long time and she has tried to help him.
"It's a tragedy that this happened and it certainly could have been stopped. This person should have been sectioned. He was arrested last week for threatening to kill her and he has been let out to do just that.
"Someone, somewhere is accountable for what has happened. Something should have been done."
Ms Raja said she had visited Ms Slack, who had started a new relationship with another man, last month.
Speaking as she laid flowers at Ms Slack's country cottage, she added: "I just want to send my love to Rachael's family. I am still in shock, we all are really. She was one of the most caring people you could imagine.
"We came to stay with her last month and we have never seen her as happy as she was then.
"In the last few months she had found happiness again with somebody else."
One school friend, a 38-year-old man, also arrived at the house this morning to lay flowers. He said Ms Slack grew up in Ripley and attended Mill Hill School before leaving the area.
He said: "She was a beautiful, bright person. This is such a tragedy. She was clever and artistic and she had a lovely beautiful boy. He was a lovely little boy."
Earlier, a neighbour said she witnessed frenzied knife attack at Ms Slack's three-storey Victorian cottage at 11am yesterday in the picturesque village of Holbrook, near Belper in Derbyshire.
Norma Way said she saw the mother, who had worked as an artist and had lived in London, screaming for help from the window of her cottage.
The 70-year-old said: "She looked out of the side window which is front of my drive and I heard her screaming in terror.
"I was the one who called the police. She started shouting to me 'Norma, Norma, call the police'.
"The man, I couldn't see, but he had raised his arm. I went to the front door but it was locked. When the police arrived they both went in but by then the screaming had stopped."
Today there was still a police cordon around the cottage and Ms Slack's black Renault Scenic, which had a baby seat in the back, was outside.
The front door of the house was on its hinges while a kitchen window was open, splintered as police had tried to break in.
There was a steel climbing frame in the well-kept back garden and police tape around the patio entrance to the house, which is lined with well looked after flower beds.
The cottage is tucked back from the main road that runs through the village. Lined with trees and well-kept gardens, Holbrook is in a conservation area in the heart of Amber Valley, Derbyshire.
Police said they were not searching for anybody else in connection with the murder of Ms Slack and her toddler son, named after the poet W H Auden.
They discovered the estranged couple dead yesterday morning at the cottage after being alerted by Ms Way. The toddler was critically injured and taken to Royal Derby Hospital by air ambulance but later died.
Ms Slack recently moved to the area after living as an ex-pat in Spain.
A spokeswoman for Derbyshire Constabulary said: "Police can confirm that the man found dead in Holbrook yesterday had been arrested last week.
"As a result of this contact, the matter has been referred to the Independent Police Complaints Commission."
A spokesman for the IPCC said today: "In light of previous police contact with the deceased man, the matter has been referred to the IPCC by Derbyshire police.
"We are presently assessing available information before deciding what involvement by the IPCC is required in an investigation.
"We aim to make a decision as soon as possible in the wake of these awful events."
The deaths of Ms Slack and her son bear striking similarities to the murder of Tania Moore.
The 26-year-old from Alkmonton, near Ashbourne, Derbyshire, was shot dead by her 36-year-old ex Mark Dyche in March 2004.
The IPCC found that Dyche, who was sentenced in May 2005 to life in prison for the murder, harassed the talented show jumper for more than a year following the breakdown of the engagement.
He sent her harassing text messages, made threats to kill her and even orchestrated a violent robbery of her home.
Ms Moore reported the threats and violence to Derbyshire Constabulary on six occasions but they failed to protect her, the IPCC found.
In its report in November 2006, the IPCC said the response of officers had been "abysmal".
Detectives failed to launch a proper investigation into her complaints, take statements or collect forensic evidence. Seven officers were disciplined as a result.
The IPCC said at the time: "Police should have taken reasonable measures to investigate Tania's reports and they should have taken reasonable measures to protect her.
"There were failures by Derbyshire officers to follow basic lines of inquiry and to thoroughly investigate both the harassment of Tania Moore in 2003."
Police said they expected to name all three, who were found in a cottage in Well Yard, later today once they had been formally identified.
The cottage is tucked back from the main road that runs through the picturesque village.
Lined with trees and well-kept gardens, Holbrook is in a conservation area in the heart of Amber Valley, Derbyshire.
Last night, neighbours described the deaths as a "terrible tragedy".
Andrew West, 52, landlord of the Spotted Cow, said the woman was a regular visitor to the pub.
He said: "She was intelligent and obviously educated. She said she had looked at a couple of places and then settled on one here."
His wife Fiona West-Hunt added: "All the police cars came around 11am-11.30am, about three ambulances and a helicopter.
"They just turned up out of the blue, loads of sirens and everything, which doesn't happen here. It's a very small, sleepy place.
"Somebody was walking their dog past and all they saw was somebody bringing a child out of a house and into an ambulance.
"Another ambulance arrived and didn't go for about half an hour."
Neighbour Allan Gilbert described Ms Slack as "jovial". He said: "We knew absolutely nothing about what happened until the cavalry arrived.
"The woman lived there with the baby. They hadn't been there long but would say hello. We didn't hear anything and we live only 10 yards away. It sounds like one of those domestic tragedies."
Assistant Chief Constable Dee Collins said: "Our thoughts go out to the family and friends of those who have died today.
"We are conducting a detailed inquiry and until we can be sure of what happened at Well Yard, it would be unfair to speculate about the circumstances surrounding these deaths."
Residents said Ms Slack had been expecting a child by her new partner.
Friends today placed bunches of flowers outside the house.
One message read: "We will miss you. Look after each other up there." Another read: "To Rach and Auden, such beautiful people. Rest in Peace."
Tracy Beardmore, 30, knew Ms Slack from a local baby and toddler group.
She said: "They were absolutely beautiful. She was lovely and he was a beautiful boy. It was not deserved."Reuse content