A senior bank executive from Kent conspired to defraud at least six of his clients through secret commissions applied to deals worth billions of dollars, an American court has heard.

Richard Boomgaardt, 44, of Oak Lane, Sevenoaks, a former managing director of Boston-based financial services company, State Street, was one of three men charged with conspiracy offences relating to securities trades made between February 2010 and September 2011.

The court was told how Boomgaardt - along with former executive vice president Ross McLellan and former senior managing director Edward Pennings - conspired to charge commissions worth millions of dollars on top of fees the clients had agreed to pay the bank.

This was in spite of written instructions to the bank’s traders which stated that the clients were not to be charged trading commissions.

The trio took steps to hide the commissions from the clients and others within the bank, the court heard, including by directing that the commissions not be broken out in post-trade reports.

For example, Pennings told Boomgaardt in a 2010 phone call not to talk about the plans to charge hidden commissions on one transaction “with anyone...because it’s not going to help our story."

He added: "Don’t even share it with the rest of the team, to be honest.”

Furthermore, in June 2010, McLellan and Boomgaardt requested the bank’s traders provide them with the reported daily high and low prices of securities the bank had traded for the client so they could determine the amount of the commissions to be applied to each security without attracting the client’s attention.

McLellan, 47, of Hingham, Massachusetts, was convicted of one count of conspiracy to commit securities fraud and wire fraud, two counts of securities fraud and two counts of wire fraud, while Pennings pleaded guilty to his charges in June 2017.

Boomgaardt was charged separately and pleaded guilty last July to one count of conspiracy to commit securities fraud and wire fraud. He is due to be sentenced on July 31.

Acting Assistant Attorney General John Cronan said: “State Street’s clients, including institutional investors managing pensions for retirees, entrusted McLellan and his subordinates to transition billions of dollars in assets.

“Rather than living up to the responsibility to act in their clients’ best interests, McLellan and his co-conspirators stole from these victims by charging hidden commissions and then lying about the scheme to cover their tracks.

"This conviction is a testament to the dedication of the FBI and prosecutors in the Criminal Division and U.S. Attorney’s Office to protecting innocent investors by investigating and prosecuting complex financial crimes.”