Peter Creegan, 43, from Tullydonnell Road, Silverbridge, Co Armagh, was accused of defrauding the First Trust Bank after he was arrested as part of a massive cross-border operation involving police in the north and south of Ireland.
He was detained last week and large amounts of documentation were taken from his home following a complaint by the First Trust and an anonymous source, police said.
He appeared at Armagh Magistrates' Court on Monday, alongside former Halifax employee Damien Pius Mallon, 52, from Drumconwell Road, Armagh, who is also accused of conspiring with him to fraudulently obtain money.
A detective constable told the court: "There are other individuals, witnesses and others, who the police seek to interview. It is not likely that it will last several months but certainly some weeks are required.
"Police have received a complaint from the First Trust Bank and a third party in respect of an initial complaint of £3.4m and 3.9m euro and that figure escalates at the moment."
Creegan was charged with making false representation to cause loss to the First Trust Bank, entering into an unlawful arrangement to acquire criminal property.
Alleged offences
He also allegedly conspired with Mallon to cheat and defraud and apply for a loan using false identity.
The alleged offences happened between 2006 and this year. Creegan, a married father-of-three, worked at the First Trust for 24 years but lost his job at the start of this year.
The detective constable added: "Interviews of Mr Creegan would indicate other matters which I prefer to withhold at this particular moment with a direct linkage to the investigation."
Mallon, 52, who has also worked as a financial advisor, was in charge of Halifax branches in Dungannon, Co Tyrone, and Keady, Co Armagh. His charges span the years from 2002 to 2009.
He was accused of fraudulently opening a bank account to make gain for himself or another to cause loss to the Halifax. He was also alleged to have converted criminal property and entered into an arrangement allowing the acquisition of criminal property.
Neither men, who wore dark suits and were flanked by prison guards, responded when the charges were read out before district judge Paul Copeland. He is to rule on their bail applications on Tuesday and they were remanded in custody.
Police said there was a fear of them absconding, given the large sums of money involved, and a risk to witnesses if they were released.
Creegan's home was searched last Tuesday and he has been interviewed at Antrim Serious Crime Suite.
Suspended
Paul Downey, solicitor for Mallon, told the court his client had been suspended by the Financial Services Authority.
"Mr Mallon has made full and frank admissions... some 18 tape recorded interviews. It is fair to say that it would be pointless for Mr Mallon to now attempt to contact any potential witness," he said.
He said there were 3,320 new accounts opened by the defendant in the last four years and warned it would take police a considerable amount of time to locate them. He said his client's passport had been taken by police.
Creegan's solicitor, Ciaran Rafferty, accepted they were grave matters but pointed out that bail can be granted even for those charged with murder.
He said his client, whose passport he claimed had been taken by police, had a property in Omeath, Co Louth, in the Irish Republic, but had important family connections dating back generations in Northern Ireland. He added that extradition arrangements meant the Republic was not a safe haven for fugitives.
"The scale is tipped in favour of admitting my client to bail," he added.