The life of a murderer, after the deed, is one long fight with such circumstances, and if he once loses his coolness he is himself almost as surely lost as a man who is carried away by his temper in a duel with swords.
After Folco had killed his wife and had just failed to kill Marcello, he had behaved with wonderful calm and propriety for a little while; but before long the old wild longing for excitement and dissipation, so long kept down during his married life, had come upon him with irresistible force, and he had yielded to it.

Then, in hours of reaction, in the awful depression that comes with the grey dawn after a night of wine and pleasure and play, terrible little incidents had come back to his memory.

He had recalled Kalmon's face and quiet words, and his own weakness when he had first come to see Marcello in the hospital--that abject terror which both Regina and the doctor must have noticed--and his first impression that Marcello no longer trusted him as formerly, and many other things; and each time he had been thus disturbed, he had plunged deeper into the dissipation which alone could cloud such memories and keep them out of sight for a time; till at last he had come to live in a continual transition from recklessness to fear and from fear to recklessness, and he had grown to detest the very sight of Marcello so heartily that an open quarrel was almost a relief.
If he had been his former self, he would undoubtedly have returned to his original purpose of killing Marcello outright, since he had not succeeded in killing him by dissipation.

But his nerve was not what it had been, and the circumstances were not in his favour.

Moreover, Marcello was now of age, and had probably made a will, unknown to Corbario, in which case the fortune would no longer revert to the latter.