US senator Ron Wyden has reportedly written to Swiss bank Mirabaud & Cie with regard to a tax evasion case involving a Houston software tycoon Robert Brockman.

Brockman is facing charges for evading taxes from the Internal Revenue Service (IRS) using a number of Caribbean entities, as well as Bermudian and Swiss bank accounts.

Wyde asked the bank whether it has informed the IRS about the businessman’s accounts related to the case, Bloomberg reported.

Last October, Swiss prosecutors froze about $950m in Brockman accounts at Mirabaud after he was slammed with the charges.

Wyden was quoted as saying in the letter to the Swiss bank: “I am deeply concerned by the duration and scale of this alleged tax evasion scheme, particularly the ability to hide billions of dollars offshore from the IRS for such an extended period of time.”

The Swiss bank has been asked to submit its response by 1 October 2021.

Meanwhile, Mirabaud in a statement said that it did not know about Brockman’s involvement.

The bank said that the US charges against the software tycoon makes clear that “Mr. Brockman went to great lengths to deceive Mirabaud about his real involvement in the accounts held with the bank, none of them were in his name.”

The bank is fully cooperating with the US authorities and has ‘fully implemented procedures’ to comply with requirements on reporting about US account holders, it said.

Mirabaud is not charged with malpractice in the case, which is said to be the largest tax evasion case in the US against an individual.

Brockman allegedly eluded taxes on $2bn in income over two decades.

After he was pressed with the indictment, the US authorities filed a forfeiture lawsuit seeking $78m from Mirabaud.

This money was held in an account in the name of Edge Capital Investment, an entity set up by Evatt Tamine and controlled by Brockman.

Tamine was a lawyer who worked for Brockman. He is also one of the nominees for Point Investments, which is another account set up at the Swiss lender.