The state also said it was "deeply concerned with the timeliness and depth of the incident investigation" conducted by BP.

WSJ: As CEO Hayward Remade BP, Safety, Cost Drives Clashed

But Mr Thomas said the initial investigation had "identified a number of questions and concerns which I now consider warrant further in-depth audit investigation".

BBC: Wales politics

Ms Reddrop said Tabak had also used the internet to conduct "in-depth research" on the case in a bid to "keep one step ahead of the investigation".

BBC: Vincent Tabak found guilty of Jo Yeates murder