LONDON: The gunman who carried out the Cumbria massacre was embroiled in a tax investigation into an undeclared £60,000 ($104,000) in his bank account and was facing serious financial difficulties, friends and colleagues have said.Detectives are working on the theory that Derrick Bird harboured grudges against several of his victims following disputes over money.Some of those killed in the early stages of his rampage had clashed with Bird in recent weeks, including his twin brother, David, and the family solicitor, Kevin Commons.However, Bird’s victims are thought to include bystanders he did not know.Bird shot and killed 12 people before taking his own life. Eleven other victims remain in hospital.The twins had had a rocky relationship since childhood. David’s family said that his downfall had been ”to try to help” his brother.However, the dispute is alleged to have escalated recently when David reported Derrick to the authorities for evading tax.A friend of the killer, Mark Cooper, said Bird had about £60,000 ($104,000) in undeclared and untaxed earnings in a bank account, which the tax authorities had discovered.”He was terrified he was going to go to prison,” Mr Cooper said.”It had been going on for six months but he only told me a fortnight ago. I had never seen him bothered about anything before.”Bird is understood to have been given details of his mother’s will last week, which was drawn up by David and Mr Commons.Mr Commons, who is believed to have been the first person to be killed on Wednesday, was shot in the driveway of his home.Bird then drove to his brother’s house and killed him while he was still in bed.Other victims include a real estate agent, Jamie Clark; a mother of two, Susan Hughes; a retired couple, James and Jennifer Jackson; and a part-time mole catcher, Isaac Dixon.Bird, a taxi driver, is thought to have fallen out with several work colleagues after they were accused of failing to follow rules when waiting for passengers. The drivers were also reported to have clashed during a recent holiday in Thailand after Bird paid a large amount of money to a Thai woman.At least two of the victims were employees at the Sellafield nuclear plant, where Bird worked until he was sacked and prosecuted for theft in 1990.Detective Chief Superintendent Ian Goulding, who is leading 100 detectives investigating the killings, said Bird appeared be have a motive for some of the murders but others were random.There were questions over the conduct of authorities after it emerged Bird had been granted two gun licences despite a conviction for theft. A former home secretary, Alan Johnson, said the government should consider introducing mental health checks for potential gun owners.However, the Prime Minister, David Cameron, said: ”Of course we should look at this issue but we should not leap to knee-jerk conclusions on what should be done on the regulatory front.”You can’t legislate to stop a switch flicking in someone’s head and this sort of dreadful action taking place.”Telegraph, London