How do I prove that Sarah's dead?

Hint 1 of 4:

Jack the Ripper always made headlines whenever he killed someone.

Hint 2 of 4:

And the newsstand owner on Baker Street keeps back issues of papers.

Hint 3 of 4:

So ask him for the edition which talked about Sarah's death.

Hint 4 of 4:

Holmes would never trouble himself by going to Fleet Street.  One of his 
helpers is more suited for the task.