Conversation so far:
what made it difficult?
It was one of the largest investigations by a British police force and predated the use of computers.
What else made it difficult?
Information on suspects was stored on handwritten index cards.
Aside from difficulties in storing and accessing the paperwork.
What did it do to the floor?
the floor of the incident room was reinforced to cope with the weight of the paper.
Why did the officers struggle?
it was difficult for officers to overcome the information overload of such a large manual system.

Question: How many times did the interview Sutcliff?
Self-contained rewrite: How many times did the West Yorkshire Police officers interview Sutcliff?