Conversation so far:
What made Peter Sutcliffe investigation difficult?
It was one of the largest investigations by a British police force and predated the use of computers. Information on suspects was stored on handwritten index cards.
What else made Peter Sutcliffe investigation difficult aside from being a large investigation predating the use of computers?
Aside from difficulties in storing and accessing the paperwork, it was difficult for officers to overcome the information overload of such a large manual system.
What did the difficulties in storing?
The floor of the incident room was reinforced to cope with the weight of the paper.
Why did the officers struggle during the Peter Sutcliffe investigation?
All information the police had about the case was stored in paper form, making cross-referencing difficult.

Question: How many times did they interview Sutcliffe?
Self-contained rewrite: How many times did the West Yorkshire Police interview Peter Sutcliffe?