Police attempting to establish the motive behind Derrick Bird's shooting rampage have said he was subject to an ongoing tax investigation.
Detectives said they are focusing on a number of key issues, including suggestions he was involved in disputes with fellow taxi drivers.
No suicide note or 'hit list' has been found during a search of his home.
The senior investigating officer, Supt Iain Goulding, said a large amount of paperwork had been taken from his house in Rowrah.
"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," he said.
"We have also been reviewing his finances and investigating issues of taxation.
"We can confirm that Derrick Bird was subject to an ongoing investigation by Her Majesty's Revenue and Customs.
"While we continue to investigate these issues, we may never fully understand what could have driven Bird to commit such atrocities as he is no longer here to answer our questions."
Meanwhile, despite reports that Bird had fallen in love with a young prostitute in Thailand, one cabbie today said the killer was more interested in drinking than women.
Mark Cooper (45) speaking from the Duke Street taxi rank in Whitehaven where Bird attacked his colleagues, said his former friend was so drunk on one flight to Thailand he was kicked off it.
He said: "He loved Thailand. He went three times last year and on the final one he got that drunk he was chucked off in Dubai.
"They were going to let him fly on the next day but he didn't bother and came home.
"He didn't bat an eyelid about it. He said: 'It was free drink – what could I do?'
"He liked his drink more than his women. I don't think he had been causing trouble on the flight because he never caused trouble.