How did Dr Jekyll reassure MR Utterson about Hyde's reaction to the Carew Murder Case?Was Utterson satisfied at the end?Why?

From the text:

The doctor shuddered. "They were crying it in the square," he said.
"I heard them in my dining-room."

"One word," said the lawyer. "Carew was my client, but so are you, and I want to know what I am doing. You have not been mad enough to hide this fellow?"

"Utterson, I swear to God," cried the doctor, "I swear to God I will never set eyes on him again. I bind my honour to you that I am done with him in this world. It is all at an end. And indeed he does not want my help; you do not know him as I do; he is safe, he is quite safe; mark my words, he will never more be heard of."

The lawyer listened gloomily; he did not like his friend's feverish manner. "You seem pretty sure of him," said he; "and for your sake, I hope you may be right. If it came to a trial, your name might appear."

The lawyer is not really reassured by Dr. Jekyll's proclamation, but the subsequent letter does provide him with satisfaction.

"No," said the other. "I cannot say that I care what becomes of Hyde; I am quite done with him. I was thinking of my own character, which this hateful business has rather exposed."

Utterson ruminated a while; he was surprised at his friend's selfishness, and yet relieved by it. "Well," said he, at last, "let me see the letter."

The letter was written in an odd, upright hand and signed "Edward Hyde": and it signified, briefly enough, that the writer's benefactor, Dr. Jekyll, whom he had long so unworthily repaid for a thousand generosities, need labour under no alarm for his safety, as he had means of escape on which he placed a sure dependence. The lawyer liked this letter well enough; it put a better colour on the intimacy than he had looked for; and he blamed himself for some of his past suspicions.