Bloomberg News says that it has taken disciplinary action against some staffers after the outlet prematurely published a story on the prisoner swap with Russia that saw journalist Evan Gershkovich freed last week.

Bloomberg editor-in-chief John Micklethwait told employees about the decision Monday morning in a memo, which was viewed by The Hollywood Reporter. Micklethwait added that he had personally written letters to all of the prisoners involved in the swap apologizing for the mistake.

Gershkovich, a Wall Street Journal reporter, was freed last week alongside fellow journalist Alsu Kurmasheva and former Marine Paul Whelan, among others, in an elaborate prisoner swap involving the U.S. and other countries. Many news outlets including Bloomberg had been briefed on the swap under a strict embargo that would lift once the swap was completed.

However Bloomberg published a story while the planes were still en route to the airfield where the swap was scheduled to take place.

Even if our story mercifully ended up making no difference, it was a clear violation of the editorial standards which have made this newsroom so trusted around the world, Micklethwait wrote, after noting that the investigation from Bloombergs standards editor had been completed.

The editor added that Bloomberg will review its processes to ensure that a similar situation does not happen again.