You say "Jack the killer." After reading the day 14 story, Jack might not yet be murderer...the new day 12 of the other story line I agree that he is the murderer...but is he working alone?
There is the part that he asks you about the butler, and when you tell him he is alive and well, he gets gloomy...as if he was expecting him to be dead.
What I will give you is Jack definitely seems to be an evil character and could definitely be the cause of future killings. He also is seen on the phone relaying information to someone (I assume someone in Orlando's family).
If anything, this tells me more that it is probably Orlando.