A British taxi driver was being investigated by tax officials before he fatally shot 12 people including his twin brother, police said on Saturday.
Derrick Bird, 52, also may have feuded with his family and colleagues before the killing spree, police said. Bird killed his brother David and a family lawyer before departing on a 45-mile rampage across a rural area of northern England, targeting former workmates and strangers. Police said he killed 10 victims in a single hour, shooting many in the face. Bird drove through narrow country lanes in his cab to evade police, firing from the window as he passed victims. He shot himself dead Wednesday in remote woodland as officers closed in. "Detectives are focusing on several key areas and are working to verify suggestions that Bird was involved in personal disputes with fellow taxi drivers, or others," Det. Chief Supt. Iain Goulding, the senior investigating officer, said on Saturday. Officers said Bird had reported he was the victim of assault in 2002 and 2007, complained about criminal damage to his taxi in 2008 and a theft from his taxi in 1998.
Goulding said the gunman's financial affairs were being investigated for possible irregularities by Britain's tax department. Friends have suggested Bird may have been motivated to kill by a feud with his brother over the proceeds from their father's will.
Mark Cooper, a friend, said the cabbie had told him he feared going to jail over the investigation by tax authorities. "We have also been reviewing his finances and investigating issues of taxation," Goulding said. But the officer cautioned that police "may never fully understand what could have driven Bird to commit such atrocities as he is no longer here to answer our questions."
Officers said they have seized documents from Bird's home, but have not recovered a suicide note.
A total of 11 people were seriously wounded during Bird's rampage on Wednesday across the northern county of Cumbria, about 350 miles (560 kilometers) northwest of London.
The dead included former colleagues at the Sellafield nuclear power plant, where Bird was dismissed for theft.
Other killed were a farmer trimming hedges in a field, a man on his bicycle, a retired couple and a woman carrying her shopping. Police said Bird held licenses for both of the weapons - a shotgun and a .22-caliber rifle with a telescopic sight - that were recovered beside his body.
Prime Minister David Cameron, who visited the region Friday, has resisted calls for any "knee-jerk" changes to the country's already stringent gun laws.
Rules on gun ownership were tightened after two massacres in the 1980s and 1990s. In 1987, gun enthusiast Michael Ryan killed 16 people in the English town of Hungerford. In 1996, Thomas Hamilton killed 16 children and a teacher at a primary school in Dunblane, Scotland.