Berean Standard Bible (BSB)
The soldiers planned to kill the prisoners so none of them could swim to freedom.
World English Bible (WEB)
The soldiers’ counsel was to kill the prisoners, so that none of them would swim out and escape.
Strong's King James
And{G1161} the soldiers{G4757}' counsel{G1012} was{G1096}{(G5633)} to{G2443} kill{G615}{(G5725)} the prisoners{G1202}, lest{G3361} any of them{G5100} should swim out{G1579}{(G5660)}, and escape{G1309}{(G5630)}.
The F.O.G *
(42) Now the soldiers' plan was to kill the prisoners, so that nobody would swim away escaping.
The F.O.G Message *
Young's Literal Translation
And the soldiers’ counsel was that they should kill the prisoners, lest any one having swam out should escape,