As far as I know - the 100yr rule would apply to sight/release of those records You may be able to locate an inquest or coroners record at Liverpool RO which may give some info
Register with https://www.britishnewspaperarchive.co.uk/account/registerYou get 3 page views free when you register.You need Liverpool Echo 14 December 1982, page 7, final columnand Liverpool Echo 14 June 1962 page 3 final column re previous serious offences
My understanding is that most deaths in custody go to inquest, the death certificate will show the cause of death. The inquest may be reported in the paper.