At first Griffin mostly confines himself to petty crimes like robbery to support his research. Then, however, as his belief in his own preeminence grows, so too does his willingness to hurt others- physically as well as financially. He becomes willing to violently assault- and even kill- anyone who stands in between him and what he wants or who seeks to hinder his plans. Near the end, maddened with rage and drunk on his own power, Griffin murders a man not because he was a threat to him in any way, but simply because he can. The less Griffin regards his fellow men as people, the more inhuman he becomes himself.
"The man's become inhuman, I tell you... I am as sure he will establish a reign of terror- so soon as he has got over the emotions of this escape- as I am sure I am talking to you. Our only chance is to be ahead. He has cut himself off from his kind. His blood be upon his own head."
It is a dark statement of intent, but Griffin has brought his violent and bloody fate on himself.
Griffin's single-minded pursuit of his research at any cost also leads to questions about the wisdom of practicing science without ethics or boundaries. Wells contrasts the two men of science in the novel: Griffin, who conducts his experiments with little thought or care as to how his methods will adversely affect those around him, and Kemp who, as a doctor, obviously believes that one should "first do no harm."
In the end, Griffin's hubris and villainous brutality bring about his downfall; his violence provokes his victims to respond equally violently, and his arrogant assumption of superiority leads him to erroneously conclude that he cannot be bested. The Invisible Man dies by the same violence he espoused and the sight of his newly visible body- naked and broken- reveals that, whatever superiority of intellect and ability he possessed, whatever villainy he was capable of, in the end Griffin was a man like any other- flawed, fallible, and very mortal.