Answer: He is horrified Mr. Hyde has murdered Carew.
Explanation:
I'm not sure what part of the book you are at but this is the most prominent part in the book where Dr. Jekyll has the most options to possibly infer.
"Utterson, I swear to God," cried the doctor, "I swear to God I will never set eyes on him again. I bind my honor 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."
