The head of security at Barclays faces an internal disciplinary probe over his part in a whistleblowing inquiry, the BBC understands.
UK financial regulators have opened an investigation into Barclays boss, Jes Staley, over the whistleblowing case.
Mr Staley asked the bank's security chief, Troels Oerting, to find the author of an anonymous letter.
The letter questioned the past conduct of a senior recruit, Tim Main, who was a former colleague of Mr Staley.
The Barclays chief executive had worked with Mr Main for several years while they were at the investment bank JP Morgan.
Mr Staley has now received a formal reprimand and a personal financial penalty - which could exceed £1m - from his own board.
Mr Oerting formerly worked for Europol and is more familiar with being asked to tackle issues of fraud, money laundering and cyber crime.
As one insider put it: "He's a former cop - he calls other cops".
The anonymous letter had a US postmark and Mr Oerting contacted US federal law enforcement agencies to help track down its origin.
His enquiry has attracted the attention of the Department for Financial Services in the US.
He joined Barclays in 2015 after heading up Europol's Cyber Crime Unit. The BBC is awaiting comment from Mr Oerting.
The attempt by Mr Staley to identify the person who sent the anonymous letter has been referred to the Financial Conduct Authority, and the Prudential Regulation Authority, as a potential breach of strict new rules concerning the treatment of whistleblowers.
Mr Staley has admitted he made an error of judgement by getting too personally involved in a matter which should have been left to bank compliance staff.
He has apologised to the board and tried to explain himself in a letter to staff.
Mr Staley told Barclays employees that he mistakenly did not consider the issue as one of whistleblowing, and instead saw it as an attempt to maliciously smear someone with previous personal problems.
The BBC understands that the anonymous letter did not raise any issues of which the personnel department at Barclays were unaware before Mr Main was hired.
The whole episode is an unusual and unwelcome distraction for a bank that is trying to put reputational problems behind it.
The bank's board held a four hour meeting on Sunday to consider the appropriate penalties for Mr Staley - including his potential dismissal.
Mr Staley is popular within the firm and with investors.
Whether that, and the penalties already imposed on him, will be enough to pacify regulators who value, and protect, whistleblowers is yet to be seen.