Police returned a number of shotguns to a dog breeding farm seven months before a mother and daughter were shot dead there.
A man, named in reports as 82-year-old dog breeder John Lowe, is suspected of fatally shooting the two women and four dogs at Keepers Cottage Stud in Farnham, Surrey.
It has emerged that a shotgun licence and a number of licensed shotguns were seized from the property last May - but returned two months later.
The police watchdog, the Independent Police Complaints Commission (IPCC), is now looking at the previous contact Surrey Police had with the parties involved and whether an investigation should follow.
A police spokesman said: "Surrey Police had had previous contact with parties involved in this incident and has referred a past contact to the IPCC.
"In May 2013 a shotgun licence and a number of licensed shotguns were seized from the address, however the licence and guns were returned in July 2013.
"We are in the process of establishing if one of these licensed guns was the firearm recovered on Sunday.
"Surrey Police is reviewing the return of the licence to ensure compliance with Home Office guidelines and has referred this matter to the IPCC."
Armed police were called to the property at 10am on Sunday.
The body of one woman was found inside, while the body of the other woman was found outside near animal pens to the back of the house.
The victims were named as Christine Lee, 66, and her daughter Lucy, 40, according to the Sun.
Stacy Banner, 38, who is Lucy's sister and Mr Lowe's stepdaughter, told the newspaper: "I have lost everyone - my mum, sister and dad. Now it seems he's wiped out my entire family. This is a nightmare.
"I just can't get my head around what's happened. My family's gone and I'm absolutely devastated."
The women have not been formally identified but they were related and known to Mr Lowe. Both died from gunshot wounds, Surrey Police said, and post-mortem examinations were due to be completed last night.
No one else was at the property at the time and a long-barrelled firearm was recovered from the scene.
Three German shepherds and a labrador were also shot and were removed from the property by the RSPCA, which also rescued a number of other animals.
The RSPCA confirmed that it had made a number of visits to the property over the last few years, including visits with other agencies.
A spokesman for the charity said: "The RSPCA is aware of the situation and working with police to ensure the welfare of the animals involved.
"We have already removed one cat and 10 dogs, including a number of puppies, from the property. These include Chihuahuas, pomeranians, shih tzus and an Old English sheepdog-type.
"Today we will be removing a small number of exotic birds from the property. At present our staff are caring for a large number of chickens at the property and we have bought in our specialist equine workers to ensure the health and welfare of four horses.
"We are currently working with other agencies to make arrangements for their long-term care."
Mr Lowe had previously been convicted of illegal puppy farming several years ago, according to reports.
In 2004 he was the subject of an investigation by the BBC's Inside Out programme, which claimed that he was breeding scores of dogs and selling puppies in poor condition.
Magistrates last night granted police a further 24 hours in which to question him on suspicion of murder.
Detective Chief Inspector Mark Preston said yesterday that the three people involved "are all believed to be known to each other and police are not looking for anyone else in connection with the incident".
He added: "It is extremely sad that two people have lost their lives and police family liaison officers are working to support their relatives and friends at this very difficult time.
"We are conducting a full and thorough investigation into the circumstances surrounding these two deaths, however, at this time, we believe this is an isolated incident and there is no further risk to the wider community."
Surrey Police later formally confirmed the identities of Christine and Lucy Lee and said post-mortem examinations showed they died from gunshot wounds.