John Gill Commentary Acts 25:4

"Howbeit Festus answered, that Paul was kept in charge at Caesarea, and that he himself was about to depart [thither] shortly." — Acts 25:4 (ASV)

But Festus answered, that Paul should be kept at Caesarea ,
&c.] Or that he was kept there, and was in proper custody, under the care of a centurion, and should continue there; nor was there any reason why he should be removed, especially since he should return thither speedily, as he adds:

and that he himself would depart shortly thither ;
the answer was a very wise and prudent one, and the reasons given were just and strong; as that Paul had been sent to Caesarea, was left bound by his predecessor there; there he found him, and there he was under a proper guard, and there it was right for him to continue; and besides, he himself should make no stay in Jerusalem, but should depart for Caesarea in a few days, and therefore it was very improper to send for Paul thither.