West Mercia police had been accused by the brother of Christopher Foster of failing to fully investigate the circumstances which led him to shoot his wife Jillian, 49, and his daughter Kirstie, before burning down their five-bedroom mansion, Osbaston House, in Shropshire, and slaughtering the family's three horses and four dogs.
Foster's body was found lying on top of his wife, having died of smoke inhalation during the conflagration which destroyed the building in August 2008.
An inquest into the deaths heard that Foster's pipe insulation business had collapsed, leaving him with debts of £4.4 million, and that he had previously told friends he would not let liquidators take his possessions, vowing "they will carry me out of the house in a box".
Following the deaths, Foster's brother Andrew accused West Mercia of allowing him to keep his shotgun licence - and later awarding him another firearms licence for the 2.2 rifle with which he went on to kill Jill and Kirstie - despite knowing he had threatened to kill a business partner he accused of trying to blackmail him.
Mr Foster, 49, of Wolverhampton, said he has been shown transcripts of a conversation in which his brother's business partner reported the threats made against him to a police officer.
He said: "If police had revoked Chris's firearms licences it would have removed one means for him to kill, and Jill and Kirstie might well still be alive today. It would certainly have acted as a warning to Jill that something was seriously wrong."
But a report conducted on behalf of the Independent Police Complaints Commission (IPCC) by West Mercia police into its own handling of the case, stated: "A full review into Christopher's access to firearms took place. There was no evidence to refuse any licences he had at the time they were renewed/reviewed. The fact that Christopher was the victim of a blackmail case would not have prevented him from being granted a firearms certificate."
The report comes as Foster's family released previously unseen photographs of him with Kirstie and his wife. The poignant set of pictures show the smiling teenager on holiday with her parents, celebrating her 14th birthday and spending time at home with her beloved horses. The inquest heard that Foster shot Kirstie in the back of the head as she slept.
The 33-page police report, obtained by The Sunday Telegraph, refuted claims by Andrew Foster that police had acted inappropriately at various stages during their investigation into the deaths. Mr Foster, a product development manager for a milk and butter dairy in Wales, complained he was not kept fully informed of developments in the investigation and that officers displayed a lack of sensitivity towards him and his mother, Enid.
Mr Foster accused the police of making it difficult for him and his wife Pam to visit Osbaston House in order to pay their last respects to his brother, Jill and Kirstie, and of allowing a film crew access to the house without his full consent.
He also complained that officers had been too quick to assume Foster had carried out the killings because of his financial difficulties, without investigating other possible motives or suspects.
West Mercia rejected each of Mr Foster's 63 complaints, saying there was no evidence its officers had breached professional standards.
Writing to Mr Foster's solicitor, Superintendent Stephen Eccleston, of West Mercia's Professional Standards Department, said: "Whilst I have come to the view that there is not enough evidence to support the detail of your complaints, I do not want to emphasise that this is not because I doubt what was said by Mr Foster. My decision simply reflects the fact that there was not sufficient independent evidence in this case for me to say the officers acted inappropriately."
Mr Foster dismissed West Mercia's report into his complaints as "a whitewash". He said: "I feel completely let down by the system. It's not an independent report, it's a case of a police force investigating itself. The report shows no empathy for us. It should have been about how two innocent people lost their lives and an opportunity to learn what lessons police could take from that."
The IPCC said Mr Forster had agreed to West Merica police carrying out the investigation into his complaint and said he was free to appeal against the report's findings.
