How does Mr. Utterson's conversation with Dr. Jekyll increase the mystery over the relationship with Mr. Hyde?From the chapter, "Dr. Jekyll was...

In this chapter, Utterson goes to talk to Dr. Jekyll in an
attempt to find out what is going on with him and Hyde -- why he has written the will
the way he has.  But his conversation with Jekyll really only makes things
worse.

This is because Jekyll does not really tell him
anything.  He tells Utterson that it is a private manner and he should leave it alone. 
But at the same time he talks about how he can get rid of Hyde whenever he wants.  And
all the time, he has a "certain incoherency of manner."

So
Jekyll is sort of just babbling a bit and doesn't really give Utterson any more
information.