Most of the evidence against Dr. Jekyll, to suggest that he is as or more guilty than Mr. Hyde for the crimes committed by Mr. Hyde, can be found in chapter 10, which comprises his own statement of the case.
In chapter 10, Dr. Jekyll describes his reasons for creating the potion that would transform him into Mr. Hyde. He acknowledges that he made the potion in part so that "the unjust might go his way, delivered from the aspirations and remorse of his upright twin." The "unjust" here represents the part of Dr. Jekyll that became Mr. Hyde, and the "upright twin" represents Dr. Jekyll's conscience. In other words, Dr. Jekyll here admits that he wanted to be able to commit "unjust" acts without his conscience nagging at him to stop.
Later in the same chapter, Dr. Jekyll says that, often, having committed a crime in the form of Mr. Hyde, he would, having returned to his own form, as Dr. Jekyll, be "plunged into a kind of wonder at my vicarious depravity." The word "vicarious" here is key. This word means that Dr. Jekyll carried out, in the form of Mr. Hyde, crimes that he himself wanted to experience. As a parent with unrealized ambitions to become a professional basketball player might live vicariously through the child by pushing that child to become the same, so to Dr. Jekyll lives vicariously through Mr. Hyde to experience the thrill of sinful behavior that is is unable to realize himself, in his own form.
Dr. Jekyll even boasts about how Mr. Hyde afforded him the perfect disguise to avoid detection and capture. He says that he "could afford to laugh at suspicion," and that he could, "in a moment, like a schoolboy, strip off these lendings and spring headlong into the sea of liberties." The language Dr. Jekyll uses here is not the language of a remorseful man. It is the language of a man who enjoyed the crimes he committed as Mr. Hyde, and who also enjoyed the fact that he could get away with them. Dr. Jekyll shows few, if any signs of remorse. In fact he says that "Edward Hyde would pass away like the stain of breath upon a mirror," implying that his conscience, represented in this metaphor by the mirror, barely registered at all the crimes committed by Mr. Hyde, or the guilt that such crimes might have induced an ordinary, moral man to feel. It was, after all, Dr. Jekyll who created Mr. Hyde, and who continued for so long to willingly take the potion to keep turning into Mr. Hyde.
In chapter 10 then we can see, from Dr. Jekyll's own hand, that he created Mr. Hyde because he wanted to commit "unjust" acts, that he enjoyed those crimes vicariously, and that he felt little if any remorse for committing those crimes as Mr. Hyde. This evidence alone should be enough for a jury to find Dr. Jekyll at least as guilty as Mr. Hyde.
The final, damning evidence against Dr. Jeyll can be found in Dr. Lanyon's letter, which comprises chapter 9 of the story. In this chapter, Dr. Lanyon recalls the words that Mr. Hyde spoke to him, before taking the potion that would transform him back into the form of Dr. Jekyll. Mr. Hyde has previously offered Dr. Lanyon the opportunity to remain in ignorance and not see the effects of the potion. When Dr. Lanyon gives in to curiosity, Mr. Hyde says
now, you who have so long been bound to the most narrow and material views, you who have denied the virtue of transcendental medicine, you, who have derided your superiors—behold!
And with this Mr. Hyde drinks the potion and transforms into the form of Dr. Jekyll, causing Dr. Lanyon a shock so severe that he will never recover. However, although the person before Dr. Lanyon, before he drinks the potion, appears in the physical form of Mr. Hyde, these words, quoted above, are clearly the words of Dr. Jekyll. Mr. Hyde has no reason to care about the professional rivalry between Dr. Jekyll and Dr. Lanyon. These words are the words of Dr. Jekyll, whose pride has been slighted by Dr. Lanyon's past ridicule, and the transformation performed in front of Dr. Lanyon is Dr. Jekyll's way of taking revenge. In this scene Dr. Jekyll is like the serpent in the biblical story of the Garden of Eden. He tempts Dr. Lanyon, just as the serpent tempted Eve, offering him "a new province of knowledge" that he knows Dr. Lanyon will be too curious to refuse, and knowing also that this knowledge will almost certainly lead to Dr. Lanyon's own demise. This is a vindictive act, carried out by Dr. Jekyll, in the full knowledge that the shock to Dr. Lanyon, his former friend and colleague, might be enough, as it proved to be, to bring his life to a premature end.
I would want to argue that the most important piece of evidence in this story that convincts Dr. Jekyll is his own testimony that is discovered and relayed to us towards the end. In it, we have Dr. Jekyll's own account of what happened and how Mr. Hyde, far from being some person or being exterior to himself, is very much a central part of his identity and whom is unleashed by Dr. Jekyll's own actions. Note for example the way in which Dr. Jekyll refers to what made him take the potion once again after having vowed never to take it:
I began to be tortured with throes and longings, as of Hyde struggling after freedom; and at last, in an hour of mortal weakness, I once again compounded and swallowed the transforming draught.
Dr. Jekyll goes on to relate how this action sent out "his devil" in all of its passion and anger. Dr. Jekyll is fully aware of the consquences of his actions, and he curiously states that he took the potion in "an hour of mortal weakness," clearly showing his own failings and responsibility in unleashing Mr. Hyde. Dr. Jekyll therefore has to be held accountable, to a certain extent, to the crimes of his alter ego.
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