Charles Spurgeon Commentary Acts 27:40-42

"And casting off the anchors, they left them in the sea, at the same time loosing the bands of the rudders; and hoisting up the foresail to the wind, they made for the beach. But lighting upon a place where two seas met, they ran the vessel aground; and the foreship struck and remained unmoveable, but the stern began to break up by the violence [of the waves]. And the soldiers` counsel was to kill the prisoners, lest any [of them] should swim out, and escape." — Acts 27:40-42 (ASV)

The soldiers were responsible for them. They would be held accountable if a prisoner escaped; so, with that cruelty and yet that obedience to law which was characteristic of the Roman legions, the soldiers' counsel was to kill the prisoners, lest any of them should swim out, and escape.