whereas

One thought in particular tormented him: namely, that during his journey hither he had sat so still, whereas he might, a dozen times, have plunged into the sea, and, thanks to his powers of swimming, for which he was famous, have gained the shore, concealed himself until the arrival of a Genoese or Spanish vessel, escaped to Spain or Italy, where Mercédès and his father could have joined him.

He spoke Italian like a Tuscan, and Spanish like a Castilian; he would have been free, and happy with Mercédès and his father, whereas he was now confined in the Château d’If, that impregnable fortress, ignorant of the future destiny of his father and Mercédès; and all this because he had trusted to Villefort’s promise.

Barnicot’s hall, where a sound might arouse the family, the bust was taken outside before being broken, whereas in the surgery, where there was less danger of an alarm, it was smashed where it stood.

Douglas and Barker are both in a conspiracy to conceal something; that they aided the murderer’s escape—or at least that they reached the room before he escaped—and that they fabricated evidence of his escape through the window, whereas in all probability they had themselves let him go by lowering the bridge.