in strict confidence

The Metropolitan Police told senior BBC managers about the arrest in "strict confidence" in November.

The Metropolitan Police confirmed that it told the BBC in "strict confidence" about the arrest of Edwards on 8 November.

“La Cote Basque” reads as if written by a misogynistic frat boy rather than the sophisticated Capote, but what galled Keith and her friends most was his use of sordid anecdotes they had told him in strict confidence.

“It is critical that any activities related to Project Plato, including the mere fact the project exists, be kept in strict confidence,” Chris Andrew, a J&J lawyer, wrote in an internal memo reviewed by Reuters.

You could tell Gretchen anything in strict confidence, knowing that five minutes later she would recall nothing but the play of shadows on your face.