Amar Manir, 24, from Bradford, who worked in the banking support section at Abbey House in Bradford, pleaded guilty to conspiracy to defraud when he appeared before Bradford Crown Court.
Three other men, not bank employees, also pleaded guilty to conspiracy to defraud.
The court heard that Manir had been a minor player in the conspiracy. Commenting at the end of the case, Judge Roger Scott said: “I am not satisfied that I have got the main people in the dock.”
The prosecution had said earlier that several suspects had not yet been arrested.
Prosecutor Sarah Barlow said the core of the fraud had been an attempt to access a number of high-value bank accounts. Members of the gang managed to access the system to change customer addresses and request cash transfers or withdrawals.
Evidence was given that £63,000 was stolen from one account and the total loss was estimated at £168,000. However, attempts to steal as much as £800,000 from other accounts were thwarted by bank security, the court was told.
Manir’s role in the conspiracy had been to access the accounts to check the progress of the fraud.
Judge Scott said he accepted that Manir, who was 21 at the time of the fraud in 2005, had not received any money from his actions and had been under instruction from other participants in the conspiracy.
The judge told him: “It was a very substantial and serious breach of trust.”
Amjad Hussain, 36, of Bury, was given a 12-month suspended sentence, Sajad Hussain, 29, of Oldham, was jailed for three months and Zamier Siddique, 28, of Oldham, was given two years community service for conspiracy to defraud.
Defendant, John Lord, 36, Oldham , who is currently in hospital will be sentenced at a later date.