Cumbria Police acted properly when they issued gunman Derrick Bird with certificates for three shotguns and a rifle, a review has concluded.
The taxi driver killed 12 people and wounded 11 others on 2 June, before shooting himself.
The review by Adrian Whiting of the Association of Chief Police Officers (Acpo) said existing gun licensing laws could not have prevented the tragedy.
It said Bird's actions could not have been predicted.
Bird shot his brother David and solicitor Kevin Commons close to his home in Rowrah, near Whitehaven, before going on what police described as a "45-mile rampage" across west Cumbria.
When it emerged Bird legally owned the weapons, Cumbria's Chief Constable Craig Mackey asked for an independent review to look into how the licences were issued.
It revealed Bird had come to the notice of police before the shootings.
He had previous convictions for drinking and driving which led to a fine and a 12-month ban.
He also had a conviction for theft and was given a suspended prison sentence.
But the review concluded these would not have precluded him from owning guns or ammunition.
Mr Whiting said: "I have concluded that the arrangements for firearm, shotgun and explosive certification in Cumbria are robust and that the people involved have the appropriate knowledge, skills and experience.
"There were no reasonable opportunities for the licensing system to have been the instrument of intervention to prevent the appalling offences subsequently committed."
The report said Bird had held a shotgun licence since 1974, when he was aged 16, and had successfully applied for renewal on a number of occasions - the latest in 2005.
In 2007 he successfully applied for a firearms certificate for a .22 rifle.
He had told police he wanted the guns to shoot pests, for clay pigeon shooting and for game shooting.
The review confirmed that hours before the murders Bird illegally sawed the barrel off the shotgun he used. He also used a rifle equipped with a silencer and a telescopic sight.
The review stated: "The investigation into these appalling crimes has indicated that neither the police, other agencies, nor members of the public were in possession of any information that may have been able to indicate to the police that Derrick Bird should reasonably have had his certificates revoked and his firearms seized prior to the events."
Mr Mackey said: "I wanted Derrick Bird's victims, the families of those who were killed, the local community and our police officers and staff to be confident that our firearms licensing procedures were robust and fit for purpose.
"Assistant Chief Constable Whiting's review has confirmed that Bird owned his firearms lawfully and that we could not have used our firearms licensing process to identify him as a risk or prevent the tragic shootings in west Cumbria."