A series of "very stark" failures by the probation service contributed to the murders of a mother and three children, a coroner has ruled.
Terri Harris, 35, her son John Bennett, 13, daughter Lacey Bennett, 11, and Connie Gent, 11, were murdered in Killamarsh, Derbyshire, by Damien Bendall, who was on licence, in 2021.
Their deaths were "contributed to by acts or omissions", Peter Nieto said.
After their inquests, relatives of the victims called for "decisive action".
Senior coroner Mr Nieto recorded that Ms Harris, who was pregnant, her children and their friend Connie, were unlawfully killed.
He said this was "contributed to by acts or omissions by the designated state agency for offending management in the course of Damien Bendall's offender supervision and management".
He stressed that Bendall bore "primary responsibility" for the "brutal and savage" murders, but there were "several very stark acts or omissions" by the probation service.
Bendall, 33, murdered the four with a claw hammer and raped 11-year-old Lacey in Chandos Crescent, Killamarsh, Derbyshire, on September 19 2021, and was given a whole life order in December 2022.
Weeks earlier, he was given a suspended sentence for arson, which included a curfew requirement at Ms Harris' home after being deemed a low risk to partners and children.
The inquests, which concluded on Monday, heard multiple reports over two weeks of how Bendall was managed by overworked, stressed and inexperienced probation officers, with the service facing "significant" challenges at the time.
The hearings were told Bendall said he would kill Ms Harris, and the children, if their relationship "went bad" as he was being fitted with an electronic tag, but a probation officer did not report the comment.
The probation service accepted 51 separate failings at the inquests, held at Chesterfield Coroner's Court, and accepted a catalogue of missed opportunities and lack of scrutiny concerning Bendall's supervision going back several years.
Following the inquests, John and Lacey's father Jason Bennett and Connie's mum Kerry Shelton described them as "kind and caring" children who had "their lives and futures taken away from them in the cruellest possible way".
In a statement, solicitors for Mr Bennett and Ms Shelton said: "On the day of their death, [the children] had been selling sweets to raise money for the charity, Youth Cancer Trust.
"Jason and Kerry remain traumatised by their deaths and how their children will never get to fulfil their potential or celebrate milestones in life.
"The hardest thing for them to accept is how failings by the authorities exposed their children to a serious risk of harm.
"Jason and Kerry believe that if appropriate measures had been taken their children would still be alive today.
"They're adamant that decisive action now needs to be taken to address the issues identified during the course of the inquests."
In a statement, Ms Harris' parents, Angela Smith and Lawrence Harris, added: "The probation service failed to protect and keep our family safe.
"They are now gone. This must never happen again.
"We hope that no other family has to live through the trauma that we have to every day."
Ms Harris' parents added: "Bendall is a violent and dangerous high-risk offender with a history of domestic abuse and risk to children.
"Despite knowing this, the probation service told the courts that it was safe for him to be curfewed to our Terri's house.
"No-one from the probation service spoke to Terri to warn her about the dangers he posed to her and the children. If she had known about how dangerous he was she would never have had any involvement with him."
Outlining his findings, Mr Nieto said a report by a probation officer leading to the curfew requirement was "wholly inadequate and misleading" and that was part of a "profoundly and seriously flawed" process.
The coroner said Bendall had a history of serious and violent offences dating back to 2004.
In addition, allegations of domestic abuse against a former partner and inappropriate contact with a young girl in care were missed due to a "failure to demonstrate sufficient professional curiosity".
The chief probation officer for England, Kim Thornden-Edwards, had previously told the inquests she acknowledged "in full" that errors had been made handling Bendall's case but that the service had suffered "significant disruption at the time" with staffing gaps.
While Mr Nieto acknowledged the impact of changes to the probation service in the months before the murders and of Covid-19, he said: "They don't explain the totality of the acts or omissions or failures of the probation service's overview and supervision of Damien Bendall and the decisions made."
He said he would prepare a prevention of future deaths report outlining concerns he identified during the inquests and require the probation service to address them.
After the hearing, lawyer David Sandiford - who represented the probation service during the inquests - said: "We extend afresh our deepest sympathies to the relatives of Terri Harris, Lacey Bennett, John Paul Bennett and Connie Gent, and indeed to all those who mourn them.
"Damien Bendall is rightly serving a whole life order.
"We recognise that the changes made with a view to ensuring that this doesn't happen again can never undo the terrible loss or assuage the grief of those whose lives will never be the same again."
