The IRS issued a rare apology to billionaire investor Ken Griffin for releasing his tax records to the press, as well as to other taxpayers whose information was breached, the tax agency said in a statement on Tuesday.

“The Internal Revenue Service sincerely apologizes to Mr. Kenneth Griffin and the thousands of other Americans whose personal information was leaked to the press,” the IRS said.

The apology stems from the case of a former IRS contractor named Charles Littlejohn, who was sentenced earlier this year to five years in prison for unauthorized disclosure of tax returns. Littlejohn had provided tax return information for Griffin and other wealthy Americans to nonprofit news organization ProPublica. 

In a statement to CBS MoneyWatch, Griffin said, “I am grateful to my team for securing an outcome that will better protect American taxpayers and that will ultimately benefit all Americans.” 

Beginning in 2021, ProPublica published a series called “The Secret IRS Files,” which included the details of tax returns for thousands of rich taxpayers, including Amazon founder Jeff Bezos and Tesla founder and CEO Elon Musk. The coverage explored how some of the wealthiest Americans minimize their taxes.

Littlejohn “violated the terms of his contract and betrayed the trust that the American people place in the IRS to safeguard their sensitive information,” the agency said in Tuesday’s statement. “The IRS takes its responsibilities seriously and acknowledges that it failed to prevent Mr. Littlejohn’s criminal conduct and unlawful disclosure of Mr. Griffin’s confidential data.”

Griffin, the founder of the hedge fund Citadel, is worth almost $42 billion, making him the world’s 34th richest person, according to the Bloomberg Billionaires Index. The IRS’ apology comes after Griffin on Monday dropped a lawsuit against the agency and the U.S. Treasury Department that he had filed in December over the breach. 

ProPublica didn’t immediately respond to a request for comment. 

The IRS said it has made “substantial investments in its data security to strengthen its safeguarding of taxpayer information.”

It added, “The agency believes that its actions and the resolution of this case will result in a stronger and more trustworthy process for safeguarding the personal information of all taxpayers.”