Taxi driver Derrick Bird sparked a massive police manhunt when he went on the rampage in west Cumbria in June, shooting dead 12 people and injuring 11 others.
His catastrophic and violent actions caused universal disbelief in the area, where he was known by many.
Bird, 52, of Rowrah - known as "Birdy" - was divorced with two grown-up sons and had become a grandfather in the weeks before the shootings on 2 June.
All accounts from friends, family, neighbours and colleagues, have described him as "quiet", "popular" and "a laugh".
And yet something made him shoot dead his own twin brother, David, then others known to him, such as the family solicitor and a colleague. He went on to kill and maim again and again, apparently at random, before taking his own life.
'You won't see me again'
Reports have circulated of a possible feud within his family or at work. But no-one has yet spoken of a man who showed any sign of being capable of mass murder, and police have said he had no history of mental illness.
His elderly mother, Mary Bird, was said to be "stunned" after learning the news that her son had murdered his twin and 11 others - Bird's brother's daughters have denied reports of any family feud.
A friend of Bird's, Peter Leder, told CNN that he was "an outgoing, well-known guy, who everyone liked".
But he said when they spoke, Bird told him: "You won't see me again."
Glenda Pears, manager at L&G Taxis in Whitehaven, said both Bird and one his victims - Darren Rewcastle - had been self-employed drivers and friends.
Ms Pears said Bird had been a taxi driver for 23 years and was a "real nice man".
She said one of her drivers witnessed the aftermath of the shooting in Whitehaven.
"The lad that's been killed [Darren Rewcastle] was friends with him. They used to stand together having a craic on the rank. He was friends with everybody and used to stand and joke on Duke Street."
One Whitehaven taxi driver - who did not want to be named - said he had known Bird for 10 years. He said he believed he had lived in the Whitehaven area all his life but that he rarely spoke of his family.
The man said Bird enjoyed foreign holidays, travelling to Thailand each year with friends. Others said he loved "tinkering" with his car and was a fan of motor sports and scuba diving.
He had not been aware of Bird owning a gun, or being a member of any gun club, he said. A neighbour also said he had never seen Bird carrying a gun but added that game shooting was not uncommon in the area.
The driver added: "He was a nice guy. He was quiet but we used to have a laugh. He was quite a friendly person."
Although some appeared to be unaware of his gun ownership, it later emerged that Bird obtained a shotgun licence back in 1995, and a firearms licence for a .22 rifle in 2007.
Police trawling through Bird's history said they now knew he had been dismissed from his job as a joiner at the Sellafield nuclear plant in Cumbria in 1990 after being convicted of stealing from his employer.
He received a 12-month suspended sentence, which - in accordance with the law and Home Office guidance - did not prohibit him from getting the gun licences.
A review published on 2 November concluded that Cumbria Police acted properly when it issued the licences, and existing gun licensing laws could not have prevented the tragedy.
The independent review, by Adrian Whiting of the Association of Chief Police Offiers, also said that Bird's actions could not have been predicted.
A similar view was held in the aftermath of the killings by friends unable to fathom his behaviour.
Michelle Haigh, the landlady of Bird's local pub, the Hound Inn in Frizington, described him as a "normal bloke".
He would often stop off at the pub, which is about three-quarters of a mile from his home, she said.
"He was a nice guy, nothing out of the ordinary. He would come into the pub, have a couple of pints, have a chat with his friend and go home.
"This is not in character with the Derrick Bird we know."
The landlady, 41, said no-one she had spoken to could think of any trigger for the fatal events.
A neighbour told the BBC Bird had lived on Rowrah Road for about 20 years and had never caused any problems, adding: "I know him, he's all right".
Whitehaven councillor John Kane told the BBC Bird had always appeared to be "very placid... a very quiet man... kept himself to himself".
He added that "Something must have pushed him over the edge."
Sue Matthews, a telephonist at A2B Taxis in Whitehaven, said the gunman lived alone, adding that he was a "quiet fellow".
"I would say he was fairly popular. I would see him once a week out and about," she said.
In his home village of Rowrah, near Frizington, shocked neighbours were still coming to terms with what had happened.
Neighbour Ryan Dempsey, 26 - who lives next door but one - said Mr Bird was "very approachable" and would often sit on his front step, drinking tea and talking to passers-by.
He said he had never seen him angry or losing his temper.
"Nobody could have a bad word to say against him, as far as I know," he said.
However he said other neighbours had remarked that on Wednesday morning he had not been his usual friendly self, and had "looked straight through people", he said.