The HSBC bank in Borehamwood lost nearly £10,000 after a sophisticated conspiracy involving a Winchmore Hill employee.
Three attempts were made to extract cash using Alexander Green as the "inside man", St Albans crown court heard on Tuesday.
Bank worker Green, 23, had been enlisted by co-defendant Marlon Bennett, 25, who he had met at a party.
Prosecutor Irshad Shaikh said that in October last year Green received a call from Bennett who met up with him in a car driven by a man known only as "J".
Mr Shaikh told the court: "J was aggressive and asked Mr Green, who he knew worked at the HSBC, to carry out fraudulent transactions.”
Bennett was involved in sending a woman into the branch on October 24. Masquerading as a genuine customer, she tried to withdraw £9,000 cash from the account using fake documents.
She failed when Green refused to deal with her. He later received a call from 'J' asking what was going on.
The next day a second attempt to take out money was thwarted when it was discovered that the account that was targeted belonged to a customer who had died.
But on October 27, the fraudsters managed to get Green to transfer £19,000 from a customer's savings account to two current accounts.
They managed to get £9,500 from one account and £300 from another. The customers were refunded and the loss was borne by the bank.
The next day Green received a call from the bank's fraud department. Mr Shaikh said: "He cried and fell to the floor and told a colleague what happened,"
Green of Park Drive, Winchmore Hill pleaded guilty to conspiracy to steal.
Bennett of Winnington Road, Enfield was convicted of the charge after a trial in which Green gave evidence. Both men were of good character.
Jeremy Barton, defending Bennett, said he still denied he was involved.
He said he was working in the voluntary sector and had been a DJ, working at a club.
For Green, Jonathan Lynn said: "He became involved through pressure and fear.
He admitted the conspiracy immediately and became emotional and confessed. He is genuinely remorseful and ashamed."
He said he had lost his job at the bank but had found new work.
Judge Stephen Warner said: "This was a sophisticated conspiracy to steal from the HSBC. "
Jailing Bennett for 12 months, he said: "You were convicted by the jury of this offence and have shown no remorse."
He told Green he had been involved in a serious breach of trust, but said he had shown courage to plead guilty and give evidence at Bennett's trial.
He passed a 4 month jail sentence suspended for 18 months, ordered him to carry out 200 hours' unpaid work, pay £2,500 compensation the bank and a £15 victim surcharge.