Police battled on Thursday to piece together the final hours of a British taxi driver who killed 12 people in a rampage at a tourist hotspot, amid reports it was sparked by a family feud.
Derrick Bird, 52, had rowed with fellow taxi drivers, at least one of whom was shot dead, while a dispute over his ageing mother's will may also have triggered Wednesday's massacre in the Lake District in northwest England.
Police confirmed that Bird had killed his twin brother David and the family solicitor, and said they were investigating speculation that financial or personal problems had pushed the gunman over the edge.
Bird also wounded 11 people as he drove through picturesque west Cumbria, calling people over to his car before opening fire or taking pot shots from the window. The surgeon treating the victims said many had facial injuries.
The rampage ended when Bird took his own life in a wood near the village of Boot, as armed police closed in on him.
Officers recovered a shotgun and a .22 rifle fitted with a telescopic sight. Police confirmed Bird had valid licences for both weapons.
More than 100 detectives were working to retrace Bird's deadly journey through an area popular with hill walkers to establish why a man described by neighbours as a "normal bloke" caused such mayhem.
Cumbria's Chief Constable Craig Mackey said: "We have in place a major investigation to piece together a picture of what happened yesterday morning in west Cumbria, so that we can try to understand what could drive Derrick Bird to take the lives of 12 innocent people and injure 11 more."
Reports suggested Bird might have planned the attacks the night before, when he got into an argument with other taxi drivers.
"Afterwards Derrick shook all their hands and said, 'There's going to be a rampage tomorrow'," one of his colleagues told The Sun newspaper.
Other reports said an old friend of Bird's recalled that the killer had told him late Tuesday: "I won't see you again."
Reports said that Bird shot the family solicitor, 60-year-old Kevin Commons, at dawn and then murdered his twin brother before driving to the taxi rank in the town of Whitehaven, and shooting three of his fellow cabbies.
Two other confirmed victims of the killing spree that followed were Susan Hughes, a 57-year-old mother of two, and Jane Robinson, 66, gunned down as she delivered catalogues door-to-door.
Detective Chief Superintendent Iain Goulding, who is leading the investigation, said it appeared the taxi driver selected some of his victims deliberately and others randomly.
He said he was "absolutely determined" to find out why the spree had happened, but warned: "It may not be possible to establish all the answers because we cannot speak to Derrick Bird."
The detective said Bird had convictions for theft in the 1990s, but he had never been to prison and there was no record of him having mental problems.
Bird's elderly mother was said to be "stunned" by her son's murder of 12 people, including his brother.
Mary Bird kept saying she wanted to speak to her sons after learning of the massacre, a relative said.
People who knew "Birdy", as the killer was widely known, described a man who lived alone but was quite popular. He was divorced, had two children and had recently become a grandfather.
David Cowman, a former colleague of Bird when he worked at the nearby Sellafield nuclear power plant 15 years ago, said he was "always pleasant".
He said he thought Bird had "just flipped".
"It's just unbelievable. I just couldn't believe it at all until I saw his photograph. I just couldn't believe it. I couldn't even sense it in him," he said.
Prime Minister David Cameron said the worst shooting incident in Britain since 16 children and their teacher were killed by a lone gunman at a primary school in Dunblane, Scotland, in 1996 was "appalling".
But he warned against a "knee-jerk" reaction to calls for tougher gun laws in the wake of the killings.
"You can't legislate for a switch flicking in someone's head," said Cameron, who is due to visit the region on Friday.