"...why did he not immediately transfer to remaining balance out to either another account and if he did not hold one, to his fiance, or parents to at least mitigate any losses"
If he had, under the ridiculously impotent "money laundering" regulations which banks are compelled to follow the recipient(s) would almost certainly have, at best, HMRC making enquiries as to the source of the funds or, at worst, Plod knocking at their door. Only Russian Oligarchs can shift money around in the UK with impunity. The rest of us have to watch out and be prepared for the consequences.