In the Sherlock Holmes Adventure of the Speckled Band why does Helen move into Julia's room?

Answer 1

Holmes does this type of deduction often in the stories as he wants to find out as much as he can about the problem at hand. He needs to independently verify anything he is told, so he can definitively prove his case. Also, he apparently wants to give his client a sense that the case is in the hands of someone who knows what they are doing.

Answer 2

"I observe the second half of a return [train] ticket in the palm of your left glove. . . . The left arm of your jacket is spattered with mud in no less than seven places. The marks are perfectly fresh. There is no vehicle save a dog-cart which throws up mud in that way, and then only when you sit on the left-hand side of the driver." -- Sherlock Holmes, 'The Adventure of the Speckled Band

Answer 3

Dr Roylott told Helen it was because repairs were necessary in her room, but it seems apparent to Holmes, and likely to Miss Stoner as well, that the real reason is because Julia's room is more suited for carrying out Roylott's plan.