WHITEHAVEN, England – Derrick Bird killed his twin brother and the family lawyer, then traveled the roads he had worked as a taxi driver, killing 12 people and wounding nearly a dozen before committing suicide.

Detectives Thursday were trying to answer the elusive question: What drove the 52-year-old cabbie to commit the worst mass shooting in Britain since 1996?

“There are 23 families out there who want to know why these events happened,” Detective Chief Superintendent Iain Goulding said.

Goulding said detectives will investigate rumors that Bird had financial problems or domestic troubles. He refused to speculate on what caused Bird to shoot people he knew, like his brother David Bird and lawyer Kevin Commons, as well as others he apparently did not. People in Whitehaven described Bird as quiet and friendly.