A resentful Derrick Bird was suffering from delusional beliefs which led him to carry out "vengeful, retaliatory fantasies" in shooting 12 people dead, a leading psychologist has said.
The mass killer was said to have blamed the rest of society for his failures but rather than killing himself alone he chose to cause grief to his community from the "vantage point of his own embitterment".
Dr Adrian West came to his conclusion after he was initially called in by police days after the shootings in West Cumbria to attempt to explain Bird's actions.
The consultant forensic clinical psychologist, who has assisted in many high-profile murder cases, went on to speak to 20 of Bird's associates, including his mother and ex-partner.
He found that on the surface Bird was an "ordinary man", described by everyone as quiet and passive, but in reality was someone who accumulated grievances and never forgot them.
Giving evidence at the inquests into the deaths in Workington, Dr West said he thought the gunman targeted his own twin brother David and his solicitor Kevin Commons to get his retaliation in first over his mistaken belief they were conspiring against him.
He then carried out "vengeance" against the taxi drivers who he thought had humiliated him before committing "dreadful violence" against random strangers in a bid to achieve notoriety on the morning of June 2 last year.
Dr West emphasised though that Bird, 52, knew what he was doing as he deliberately chose his victims along his driving route and made conscious decisions not to harm certain people.
Forensic psychiatrist Dr Mark Swinton told the hearing that it was his opinion that Bird had a mental illness at the time of the incidents.
Asked by HM Coroner for North and West Cumbria, David Roberts, whether Bird could be classed as insane, Dr Swinton replied: "If he had lived I would have thought it extremely unlikely he would have been found not guilty of murder by reason of insanity."