A devastated woman has condemned police who handed back firearms to her stepfather seven months before he shot dead her mother and sister.
Stacy Banner said 66-year-old Christine Lee and Lucy Lee, 40, would still be alive had Surrey Police acted properly against John Lowe.
One of the guns returned to Lowe was used to fatally shoot the pair in a rampage at his puppy farm near Farnham, Surrey, on February 23, 2014.
Seven months before the shooting, Lowe had his shotguns and certificate seized after Mrs Banner reported to police that he had threatened to shoot her.
As the Independent Police Complaints Commission (IPCC) released a critical 76-page report into Surrey Police's firearms licensing team's handling of the case, Mrs Banner said she now plans to sue the force.
She said: "It is devastating to see your worst fears confirmed in black and white about how those entrusted with the public safety can abuse and neglect their powers. But for the police's failings, my mum and sister would be here today."
The IPCC said Surrey Police failed to consider and properly assess information relating to Lowe before returning the firearms to him.
And the police watchdog found the force's firearms licensing team lacked training and was staffed by people failing to do their duties properly.
Prosecutors ruled out criminal charges against police staff, but two firearms licensing team members had cases to answer for misconduct. John Crabb was sacked following a hearing, while Stanton Royle retired before one was held.
The IPCC found evidence that during the license review, Mr Royle and Mr Crabb did not take simple investigative steps such as accessing Surrey Police's information and intelligence systems.
The pair also did not highlight risks posed by Lowe or properly address whether he was a danger to the public when deciding to hand back his shotguns and certificate.
IPCC associate commissioner Tom Milsom said: "Our investigation paints a deeply concerning portrait of how Surrey Police's firearms licensing team operated at that time."
Recommendations have been made to improve firearms licensing locally and nationally.
The IPCC also carried out a separate inquiry into how family liaison officers dealt with Mrs Banner in the aftermath of the killings, and her subsequent arrest for which no further action was taken.
Investigators found a detective constable and a detective sergeant had cases to answer for misconduct, and a detective inspector had a case to answer for gross misconduct.
Mrs Banner's solicitor, Sarah Ricca, of Deighton Pierce Glynn, said: "The IPCC recommendations in this shocking case include that the licensing team should liaise with officers investigating allegations against firearms license holders.
"In other words, the IPCC is recommending that licensing team staff do their job. It is a vindication for Stacy Banner that staff faced dismissal proceedings and one was sacked, and that both local and national recommendations have been made."
At Guildford Crown Court in October 2014, Lowe, then aged 82, was jailed for life to serve a minimum of 25 years in jail after being found guilty of the murders.
Responding to the IPCC's report, Surrey's assistant chief constable Helen Collins said: "The safety of the public has always been our primary concern and it was extremely important to us that in light of these events, changes were made quickly and efficiently to ensure we could be confident in our decision making practices.
"In 2014, the force commissioned two independent reports from Hampshire Constabulary and North Yorkshire Police which indicated the decision by firearms licensing officers to return weapons to John Lowe was flawed and did not meet national standards. We spoke with members of Christine and Lucy Lee's family at that time to advise them of these findings and to apologise for that decision.
"As a result of those reports, we conducted a comprehensive review of our firearms licensing in the years since 2014 and instigated the recommendations from both independent reports."
Sandra Horley, chief executive of Refuge, said she supported Mrs Banner's call for a full inquest to get answers to other questions not examined by the IPCC.
She said: "Things are not changing fast enough. Stacy repeatedly warned the police about Lowe. It is a tragedy they did not take her seriously."