That's a pretty weak argument, in my book

Scotland Yard fights to keep Jack the Ripper files secret: Scotland Yard is fighting an extraordinary legal battle to withhold 123-year-old secret files which experts believe could finally provide the identity of Jack the Ripper

They say releasing the ledgers could compromise the fight against crime because people would be less likely to act as informants if they knew that at some point their identities might be released. They also said that it might put descendants of informants to rest.

You know, I've always thought that the Duke of Clarence theory was very weak, but you do have to wonder, given the refusal to release information that could finally unmask Jack the Ripper.