Why does Victor, even when faced with the prospect of seeing others injured or killed, remain silent?

Guilt seems to rule Victor for much of the novel. For example, after Justine Moritz has been found guilty of murdering William, who is Victor's brother, Victor claims that

Anguish and despair had penetrated into the core of my heart; I bore a hell within me which nothing could extinguish.

He talks a great deal about his own guilt and feelings of upset following the deaths of William and Justine, and he says that he feels terrible about the depression felt by Elizabeth and other members of his family as a result; however, he doesn't seem to seriously consider confessing to his creation of a monster. Perhaps this is because he doesn't want his friends and family to know what he's done. Perhaps it's because he feels no one will believe him; the story of the creature's "birth" is pretty extraordinary. Perhaps it's because he did commit some illegal actions, like digging up graves and raiding the bodies of the recently deceased, in the creation of his "person," and he doesn't want to go to jail. Very likely, it is some combination of all of these. Otherwise, his terrible guilt might actually compel him to confess rather than remain silent, but fear of the consequences of confession seems to keep him silent.