John Gill Commentary Acts 23:22

"So the chief captain let the young man go, charging him, Tell no man that thou hast signified these things to me." — Acts 23:22 (ASV)

So the chief captain then let the young man depart
After he had had the account from him, and was master of the whole affair:

and charged him, see that you tell no one that you have shown these
things to me ;
which was prudently said; it was a right and wise thing to conceal this matter, that the men might go on with their designs, and an opportunity be taken to convey Paul away, before the time came fixed by them to execute them; for otherwise, should it have been known that their plot was discovered, they would have entered upon new measures.