'"Henry Jekyll forge for a murderer"' What does Mr Utterson think Dr Jekyll was doing?

Jekyll also claims that he has received a letter from Hyde, which he shows to Utterson. The letter thanks Jekyll for his kindness and urges him that he need not worry for his safety, as he has a sure means of escape. Dr. Jekyll does not have the envelope, and claims that he burned it after it was hand delivered. Upon returning to his office, Utterson receives a dinner invitation from Jekyll. When the letter arrives, Utterson's assistant, Mr. Guest, is examining the writing on the letter supposedly from Hyde. Mr. Guest instantly recognizes that the same individual wrote both letters. Utterson angrily assumes that Jekyll has forged a letter for a murderer.