A taxi driver who shot dead his partner and two other women before turning a gun on himself had a licence for six firearms, despite having threatened to kill himself three years ago.
Durham Police will be the subject of an Independent Police Complaints Commission investigation after it emerged that Michael Atherton's licence was not revoked following a review of the previous incident in 2008.
Mr Atherton (42), known as Micky, was a keen game hunter and had a licence to keep three shotguns and three "section one" weapons, which require greater authorisation.
It was not known what prompted him to open fire at his home on New Year's Day, killing his partner of 19 years, Susan McGoldrick (47), her sister Alison Turnbull (44) and Mrs Turnbull's daughter, Tanya (24), before shooting himself. Friends suggested that he had been suffering from depression.
Mrs McGoldrick's 19-year-old daughter, Laura, managed to escape by leaping from an upstairs window after being shot. She left hospital after having pellets removed from her wrist and shoulder.
Two other people who were in the semi-detached house in Horden, near Peterlee, Co Durham, at the time of the shootings also survived.
Assistant Chief Constable Michael Banks of Durham Police admitted that the force had been alerted to reports that Mr Atherton had threatened to harm himself in 2008.
"We have had contact with the family," he said. "We are busy reviewing the exact circumstances around that. There was a report of a male at that address self-harming. That was some years ago."
The law states that an individual must apply to the police to hold a shotgun or other firearm.
Applicants are then supposed to be interviewed to ensure that they do not present a risk and must declare any criminal convictions, medical conditions or previous treatment for depression or mental illness.
Licences must be renewed every five years when the same checks are repeated.
A Home Office spokesman said: "The main purpose of firearms legislation has always been to protect public safety at the same time as ensuring that controls are practical and proportionate."
Firearms officers were called to Mr Atherton's home at 11.45pm on New Year's Day after several "hysterical" 999 calls were made from the house.
Detectives said the occupants had been out for the evening and had only recently returned to the house. Mr Atherton had been at the Victory Club in Horden and had been drinking, but was not said to be drunk. The three dead women are believed to have been shot immediately after returning to the house.
Steve Patterson, a family friend, said that Mr Atherton's brother, Chris, had told him just hours before the shootings that his brother had not been himself.
Mr Patterson (51) said: "Chris was saying that his brother wasn't doing too well and had been suffering from depression. He said he was fed up with the way his life was going. I think he started feeling down after an operation he had on his heart."
Neighbours described the scene of panic as Mr Atherton, who had a 17-year-old son, Micky, with Mrs McGoldrick, launched his attack, which lasted "seconds".
One said: "I was walking home from work at quarter past 12 last night and I saw was a guy running around covered in blood. He was shouting 'someone's been shot in the head'."
Another described a blood-covered man shouting "she's been shot in the head, save my girlfriend, he's shot her in the head". (© Daily Telegraph, London)